Vehicle braked with motor torque and method of controlling the same

ABSTRACT

A vehicle has a power system, in which an engine, a motor, a torque converter, a transmission, and an axle are connected in series. The transmission has a mechanism of varying a gear ratio under the control of a control unit. A driver of the vehicle operates a specific switch for setting a deceleration to specify a desired deceleration by means of power source braking. In response to an ON operation of a snow mode switch, a possible range of setting of the deceleration is restricted to a specific area that does not cause any slip or skid of the vehicle. The control unit totally controls the torque of the motor and the gear ratio, thereby implementing the braking at the desired deceleration. This arrangement attains the desired deceleration specified by the driver in the wide possible range of the setting, while restricting the deceleration to a specific range according to the driving conditions of the vehicle.

TECHNICAL FIELD

The present invention relates to a vehicle that may be braked with amotor as well as with a mechanical brake utilizing a frictional force,and also to a method of controlling such a vehicle. More specificallythe present invention pertains to a vehicle that is braked with a motorto attain an arbitrarily adjustable speed reduction rate, as well as toa controlling method to actualize such braking.

BACKGROUND ART

A hybrid vehicle with both an engine and a motor as the power source hasbeen proposed as one form of vehicles. For example, a hybrid vehicledisclosed in JAPANESE PATENT LAID-OPEN GAZETTE No. 9-37407 additionallyhas a motor placed in series between an engine and a transmission in apower system of an ordinary vehicle where an output shaft of the engineis connected with a drive shaft via the transmission. This arrangementenables the hybrid vehicle to be driven by means of both the engine andthe motor as the power source. The engine generally has poor fuelconsumption at a time of starting the vehicle. In order to avoid thedriving of poor fuel consumption, the hybrid vehicle makes a start byutilizing the power of the motor. After the speed of the vehicle reachesa predetermined level, the hybrid vehicle starts its engine and issubsequently driven by utilizing the power of the engine. The hybridvehicle accordingly improves the fuel consumption at the time ofstarting. The hybrid vehicle causes the motor to regenerate therotations of the drive shaft as electric power, which is used forbraking (hereinafter such braking is referred to as the regenerativebraking). The hybrid vehicle carries out the regenerative braking andthereby enables the kinetic energy to be used without significantwastes. These characteristics desirably improve the fuel consumption ofthe hybrid vehicle.

There are two different types of braking in the vehicle. One brakingprocess presses a brake pad against the drive shaft in response toactuation of a brake pedal, so as to apply a frictional force to theaxle (hereinafter referred to as the wheel braking). The other brakingprocess causes the power source to apply a load to the drive shaft, likeengine brake (hereinafter referred to as the power source braking). Thehybrid vehicle utilizes, as the power source braking, engine brake basedon a pumping loss of the engine and regenerative braking due to aregenerative load of the motor. The power source braking does notrequire the driver to change the foot position from the acceleratorpedal to the brake pedal for the purpose of braking. In order to enhancethe effectiveness of the power source braking, it is desirable toarbitrarily set a speed reduction rate required by the driver.

The engine brake results in a substantially fixed speed reduction rateaccording to the engine speed, unless the open and close timings of anintake valve and an exhaust valve are changed. In order to attain adesired speed reduction rate by engine brake, the driver is required tooperate a gearshift level to vary the gear ratio of the transmission andthereby change the ratio of the torque of the power source to the torqueoutput to the drive shaft. The advantage of the regenerative braking ofthe motor is, on the other hand, relatively easy control of theregenerative load, which leads to relatively easy control of the speedreduction rate.

In the conventional hybrid vehicles, however, a diversity of problems asdiscussed below arise in the braking process utilizing the motor.

The first problem is that there has been no discussion on the possiblerange of the speed reduction rate set by the driver. Namely nodiscussion has been held on the desirable range of the speed reductionrate, in order to attain the stable driving of the hybrid vehicle.

The second problem is that the speed reduction rate can be set only in avariable range of the regenerative load of the motor. In some cases, thehybrid vehicle can not sufficiently attain the speed reduction raterequired by the driver. The insufficient speed reduction rate occursespecially in the course of high-speed driving of the vehicle.

The third problem is that the driving state allowing the regenerativebraking with the motor is relatively limited. For example, when theaccumulator is in a state close to the full charge level, no furthercharging is allowed for the regenerative braking.

In such circumstances, the advantages of the power source braking, forexample, actuation of braking without any change the foot position, arenot fully utilized.

Utilizing the wheel braking to compensate for the insufficiency of thespeed reduction rate damages the advantage of the power source brakingthat does not require any change of the foot position. The wheel brakingcauses the kinetic energy of the vehicle to be consumed in the form ofthermal energy and accordingly damages the advantage of the hybridvehicle that is the effective use of energy.

In the prior art hybrid vehicle, a large speed reduction rate may beattained by operating the gearshift lever to change the gear ratio ofthe transmission. In this case, however, the speed reduction ratedrastically varies with the operation of the gearshift lever, whichresults in a poor ride..

The fourth problem is that there has been no discussion on themanipulation mechanism that allows the user to set the speed reductionrate. For the effective actuation of the regenerative braking, it isdesirable that the user can arbitrarily and readily set the speedreduction rate. The desired speed reduction rate frequently variesaccording to the driving state of the vehicle, so that the easy changeof the settings is demanded. It is, on the other hand, demanded toprevent an unintentional variation in speed reduction rate. Nomanipulation mechanisms for allowing the user to set the speed reductionrate have practically been proposed by considering such conditions.

The fifth problem is that there has been no discussion on the desiredsettings of the speed reduction rate at the respective gear ratios inresponse to the operation of the gearshift lever to change the gearratio and the specification of the speed reduction rate. In order tofully utilize the advantage of the power source braking that does notrequire any change of the foot position from the accelerator pedal tothe brake pedal and enhance the operatability of the hybrid vehicle, itis required to attain the speed reduction rate that well follows thedriver's feeling. There has been no discussion from these viewpoints howthe setting of the speed reduction rate should vary against the changinggear ratio, for example, in response to the specification of the speedreduction rate by the driver. In the prior art hybrid vehicles, there isstill a requirement for the further improvement in effectiveness of thepower source braking.

The sixth problem is that the energy recovery rate is lowered when thedriver operates the gearshift lever to changeover the working range ofthe gear ratio. In the hybrid vehicle with a transmission, the driveroperates the gearshift lever with a view to gaining a greater speedreduction rate and ensuring quick acceleration after the brakingcontrol. The driver may select a specific gearshift position where thepositions of the change-speed gear having the greater gear ratios areavailable. In other words, the driver may select the gearshift positionthat prohibits the use of the positions of the change-speed gear havingthe smaller gear ratios.

In the prior art hybrid vehicle, the quantity of regeneration by themotor is reduced in such cases. This leads to the insufficientregeneration of the kinetic energy of the vehicle in the form ofelectric power.

In order to enhance the energy recovery rate of the vehicle, the brakingcontrol may be carried out at another specific gearshift position wherethe positions of the change-speed gear having the smaller gear ratiosare available. This leads to a lesser ratio of the speed reduction rateapplied to the axle to the braking torque of the power source. Due tothis lesser ratio, the braking control by the power source braking cannot be implemented with the sufficiently large speed reduction ratedesired by the driver. The driver should accordingly use the wheelbraking to obtain the sufficient speed reduction rate. The use of thewheel braking leads to the lowered energy recovery rate. The selectionof this gearshift position does not allow the quick acceleration desiredby the driver after the braking control, thereby significantly damagingthe controllability of the vehicle.

The problems discussed above arise not only in the hybrid vehicles withboth the engine and the motor as the power source but in any vehicleswith only the motor as the power source. Similar problems are also foundin vehicles with both the engine and the motor mounted thereon; whichuses only the engine for the power source of drive and utilizes themotor for other purposes, such as regenerative braking.

DISCLOSURE OF THE INVENTION

One object of the present invention is to provide a vehicle that attainsadequate speed reduction according to driving conditions of the vehicleby utilizing a motor, and a method of controlling such a vehicle.Another object of the present invention is to provide a vehicle thatsmoothly regulates a speed reduction rate in a process of braking with amotor in a wide possible range of setting in response to an instructionof a driver, and a controlling method to attain such braking.

At least part of the above and the other related objects is attained bya first vehicle that includes a motor, a transmission that enablesselection of a plurality of gear ratios in a process of powertransmission, and a drive shaft, which are connected with one another,and is braked by means of a torque output from the motor. The firstvehicle includes: an operation unit, through an operation of which adriver of the vehicle specifies a speed reduction rate in a process ofbraking with the motor; a target speed reduction rate setting unit thatsets a target speed reduction rate in response to the operation of theoperation unit; a selection unit that selects a target gear ratio amonga plurality of available gear ratios, the target gear ratio enabling thecurrently set target speed reduction rate to be attained by the torqueof the motor; a motor driving state specification unit that specifies atarget driving state of the motor, in order to enable a braking forcethat attains the currently set target speed reduction rate to be appliedto the drive shaft; and a control unit that controls the transmission toattain the target gear ratio and drives the motor in the specifiedtarget driving state.

The target driving state of the motor is specified by a diversity ofparameters relating to driving conditions, for example, the targettorque, the electric power regenerated by the motor, and the electriccurrent flowing through the motor.

In the vehicle of the present invention, the selection unit selects anadequate gear ratio according to the speed reduction rate specified bythe driver and the magnitude of the torque output from the motor.Controlling the driving state of the motor at the adequate gear ratioensures the speed reduction rate required by the driver. The firstvehicle of the present invention totally controls both the transmissionand the motor, thereby implementing the braking in response to thespecification by the driver in a wide range.

The braking control with the torque of the motor generally works whenthe accelerator pedal is released. In the case where the power-sourcebraking does not attain the sufficient speed reduction ratecorresponding to the requirement of the driver, the driver should stepon the brake pedal, so as to make the wheel braking act and raise thespeed reduction rate. This requires the driver to change the footposition from the accelerator pedal to the brake pedal. A return of thefoot position from the brake pedal to the accelerator pedal is thenrequired for acceleration following the speed reduction. The frequentchange of the foot position worsens the controllability of the vehicle.

The first vehicle of the present invention, on the other hand,implements the braking control with the motor in a wide range of speedreduction rate as described above. A simple release of the acceleratorpedal accordingly ensures the sufficient speed reduction rate that issubstantially coincident with the requirement of the driver. The drivercan thus brake the vehicle and subsequently accelerate the vehiclewithout changing the foot position between the accelerator pedal and thebrake pedal. From this point of view, the first vehicle of the presentinvention significantly improves the controllability of the vehicle.

The first vehicle of the present invention also has advantages on theenergy efficiency as discussed below. The wheel braking utilizes thefriction of the brake pad against the drive shaft and abandons thekinetic energy of the vehicle in the form of thermal energy, so as tobrake the vehicle. This is not desirable from the viewpoint of energyefficiency. The regenerative braking by means of the motor, on the otherhand, regenerates the kinetic energy of the vehicle in the form ofelectric power. This structure enables the regenerated energy to beeffectively used for a subsequent drive. The first vehicle of thepresent invention implements the regenerative braking by means of themotor in a wide range, thereby significantly improving the energyefficiency of the vehicle.

The term ‘speed reduction rate’ in the specification hereof represents aparameter relating to the speed reduction of the vehicle. The speedreduction rate may be, for example, a deceleration, that is, a reductionrate of vehicle speed per unit time, or a braking force.

The term ‘vehicle’ in the specification hereof includes various types ofvehicles. The first type is a vehicle having only the motor as the powersource, that is, a pure electric vehicle. The second type is a hybridvehicle having both the engine and the motor as the power source. Thehybrid vehicle includes a parallel hybrid vehicle where the power outputfrom the engine is transmitted directly to the drive shaft and a serieshybrid vehicle where the power output from the engine is not directlytransmitted to the drive shaft but is used only for generation ofelectric power. The principle of the present invention is applicable toboth the parallel hybrid vehicle and the series hybrid vehicle. Thepresent invention is also applicable to the structure having three ormore engines or motors as the power source. The third type is a vehicleusing only the engine for the power source of drive but also having themotor mounted thereon for the purpose of regenerative braking.

The vehicle of the present invention may further include a braking powersource that applies a braking torque, other than the motor. In thevehicle with only the motor as the braking power source, the motordriving state specification unit sets the torque of the motor to attainall the desired speed reduction rate. In this case, a negative torque isgenerally set to the motor torque, and the motor carries outregenerative operation. In the vehicle with a plurality of braking powersources including the motor, on the other hand, the motor driving statespecification unit sets the torque of the motor by taking into accountthe speed reduction rate attained by the other braking power sources. Inthis case, the speed reduction rate by the other braking power sourcesmay be fixed to a predetermined value. Alternatively the motor torquemay be subjected to feedback control, which makes the total speedreduction rate equal to a predetermined value.

The technique of the present invention is applicable to a diversity ofvehicles having various structures.

The technique of the present invention is especially preferably appliedto the vehicle further having an engine in a specific state of linkagethat enables a braking torque to be applied to the drive shaft. In thisstructure, the selection unit selects the target gear ratio, based onthe torques of the motor and the engine, and the motor driving statespecification unit specifies the target driving state of the motor bytaking into account the braking torque applied by the engine. Thevehicle may be a hybrid vehicle that can use the motor for a drive oralternatively a vehicle that uses the motor only for the purposes otherthan a drive, for example, regenerative braking.

The hybrid vehicle typically has a motor as an auxiliary power source inaddition to the engine. The motor is used, for example, at a start ofthe vehicle or during a low-speed drive and is utilized to supplementthe insufficient torque of the engine. The parallel hybrid vehicle oftenhas a small-sized motor having a relatively low rated output suitablefor such purposes. In many cases, the motor mounted on the hybridvehicle does not have the ability to sufficiently carry out theregenerative braking required by the driver.

The conventional vehicle using the motor not for a drive but for theother purposes, such as the regenerative braking, often has thesmall-sized motor, as in the case of the hybrid vehicle. The techniqueof the present invention ensures the braking control in a wide range bycontrolling both the transmission and the motor.

This technique is especially effective in the vehicles with the motor ofthe limited rating.

In the first vehicle of the present invention, the target gear ratio isselected by a variety of methods.

In accordance with one preferable embodiment, the vehicle furtherincludes a storage unit, in which a relationship between the targetspeed reduction rate and the target gear ratio is stored. The selectionunit selects the target gear ratio by referring to the storage unit.

In this arrangement, the relationship between the target speed reductionrate and the gear ratio is flexibly specified by taking into account thestructure of the vehicle, the available range of the gear ratio by thetransmission, and the rated output of the motor. This arrangementfacilitates the selection of the target gear ratio in the brakingprocess and accordingly reduces the load of the processing.

The relationship between the target speed reduction rate and the gearratio may be specified by a diversity of settings, based on experimentsor analyses. For example, the gear ratio may be set unequivocallycorresponding to each target speed reduction rate, or alternatively aplurality of gear ratios may be mapped to each target speed reductionrate. In one example of the latter case, two gear ratios are allocatedto each target speed reduction rate. This arrangement advantageouslyenables the selection of the more appropriate gear ratio by taking intoaccount a variety of conditions other than the speed reduction rate, forexample, the driving state of the vehicle.

One embodiment changes the relationship between the speed reduction rateand the minimum gear ratio used in each driving state of the vehicle,among the relations between the gear ratio and the speed reduction rate,in response to the specification by the driver. The stationary drivegenerally adopts the minimum gear ratio. When the driver tries to changethe setting of the speed reduction rate, the driver often intends tochange the speed reduction rate during the stationary drive, that is, tochange the speed reduction rate at the minimum gear ratio. Thearrangement of varying only the setting of the speed reduction rate atthe minimum gear ratio simplifies the control procedure for attainingthe speed reduction rate in response to the operation by the driver. Inthe case where the available gear ratio range is changed according tothe driving state of the vehicle, the setting of the speed reductionrate may be varied only at the minimum gear ratio among the availablegear ratios in each driving state.

Another embodiment varies not only the setting of the speed reductionrate at the minimum gear ratio but the speed reduction rate at all thegear ratios used in each driving state of the vehicle. In the case wherethe available gear ratio range is changed according to the driving stateof the vehicle, the setting of the speed reduction rate at a certaingear ratio may not be fixed but be varied with the change of theavailable gear ratio range. For example, the speed reduction rate at thethird speed in the case of a drive using the first through the fifthspeeds may be different from the speed reduction rate at the third speedin the case of a drive using only the first through the third speeds.

The arrangement of varying only the speed reduction rate at the minimumgear ratio may be combined with the arrangement of varying the speedreduction rate at all the gear ratios. One exemplified control of suchcombination varies only the setting of the speed reduction rate at thefifth speed, which represents the minimum gear ratio, in the case of adrive using the first through the fifth speeds. The control varies thesetting of the speed reduction rate at all the gear ratios in the caseof a drive using only the first through the third speeds.

When the vehicle has a shift mechanism that enables the driver to changethe available gear ratio range used during a drive, the speed reductionrate reflecting the requirement of the driver can be attained accordingto the selection of the shift mechanism. The shift mechanism may have amanual mode that allows the driver to manually change the gear ratio. Inthe case where the change of the gear ratio is manually implemented, thedriver often requires the flexible braking and acceleration of thevehicle. In this case, the speed reduction rate may be changed to alarger value than the value selected in the case of the automaticcontrol of the gear ratio.

In the first vehicle of the present invention, a variety of structuresmay be applied to the operation unit, through an operation of which thedriver specifies the speed reduction rate in the process of braking withthe motor.

In accordance with one embodiment, when the vehicle includes achangeover unit that changes over a selectable gear ratio range for thetarget gear ratio in response to a predetermined operation by the driverof the vehicle, the operation unit has a mechanism that ensures thespecification of the speed reduction rate in response to anotheroperation of the changeover unit that is different from thepredetermined operation for the changeover.

This arrangement enables the target speed reduction rate to be setwithout unnecessarily providing any additional switch or related elementin the vehicle. The changeover unit is generally disposed in a locationthat ensures the easy access of the driver. The operation unit of thisstructure accordingly has excellent controllability in the process ofsetting the speed reduction rate. The operation unit shares thestructure with the conventionally provided changeover unit. The drivercan thus set the speed reduction rate without feeling anyincompatibility.

There is another advantage in the arrangement that the operation unitfor setting the speed reduction rate shares the structure with thechangeover unit for changing over the selectable gear ratio range. Thefirst vehicle of the present invention controls both the gear ratio ofthe transmission and the regenerative braking of the motor, therebyattaining the braking control in a wide range of speed reduction rate.In the arrangement that the changeover unit and the operation unit aredesigned to have separate mechanisms, there is a possibility that thecurrently set target speed reduction rate is not attained in the gearratio range selected by the operation of the changeover unit. In thevehicle of the above arrangement that the changeover unit and theoperation unit are designed to share a common mechanism, however, suchconflicting instructions are readily avoided. This arrangementaccordingly ensures the adequate braking control.

A gearshift lever employed in the vehicle with a conventional automatictransmission is applicable for the changeover unit. In this case, theoperation unit may be actualized by the structure that causes thegearshift lever to be operated in a movable area, which is differentfrom a conventional movable area to changeover the available range ofthe change-speed gear. In accordance with one concrete structure, when agearshift lever, which is slid along a predetermined groove tochangeover the available range of the change-speed gear, is used for thechangeover unit, the operation unit is constructed as a mechanism wherethe gearshift lever is slid along a second groove, which is provided inparallel with the predetermined groove, to set the speed reduction rate.In another example, the operation unit is constructed as a mechanismwhere the gearshift lever is slid along a rearward extension of thepredetermined groove to set the speed reduction rate. In still anotherexample, the speed reduction rate may be set by sliding the gearshiftlever while keeping a preset switch on the gearshift lever in a pressedposition, or by sliding the gearshift lever that is kept in a pull-upposition or in a press-down position.

In some vehicles with the automatic transmission mounted thereon, thechangeover unit may be provided on a steering wheel. In accordance withone embodiment, pressing a first switch provided on the steering wheelwidens the available range of the change-speed gear in the automatictransmission, whereas pressing a second switch narrows the range. Theoperation unit of the present invention may utilize the structure ofthis changeover unit. For example, the speed reduction rate may beincreased by a press of the first switch and decreased by a press of thesecond switch. The vehicle having the changeover unit provided on thesteering wheel also has a gearshift lever; in general. In the case wherethe gearshift lever is in a predetermined position to set the targetspeed reduction rate, the first switch and the second switch function toset the speed reduction rate. In other cases, the first switch and thesecond switch function to changeover the available range of thechange-speed gear in the automatic transmission. The use of the switchesprovided on the steering wheel advantageously enables the driver toquickly set the speed reduction rate while holding the steering wheelfor a drive.

In accordance with one preferable application of the present invention,the operation unit included in the first vehicle has a mechanism thatspecifies the speed reduction rate by sliding a lever along a slidegroove formed in advance. In this application, the mechanism of theoperation unit may allow the setting of the speed reduction rate to bevaried continuously according to a sliding operation of the lever. Theoperation unit may be constructed to share the structure with amechanism for inputting a gearshift position that represents aselectable gear ratio range during a drive of the vehicle. The lever forsetting the speed reduction rate may alternatively be providedseparately from the mechanism for inputting the gearshift position.

In accordance with one preferable embodiment, the operation unitincludes a first slide groove, along which the lever is slid during thedrive of the vehicle, and a second slide groove, along which the leveris slid to specify the speed reduction rate, wherein the first slidegroove and the second slide groove are disposed in series. In thisembodiment, the operation unit may have a mechanism that increases thespeed reduction rate with an increase in deviation from a movable rangeof the lever during the driver of the vehicle. In accordance withanother preferable embodiment, the operation unit includes a first slidegroove, along which the lever is slid during the drive of the vehicle,and a second slide groove, along which the lever is slid to specify thespeed reduction rate, wherein the first slide groove and the secondslide groove are disposed in parallel.

In the first vehicle of the present invention, a diversity ofarrangements may be applied to set the target speed reduction rate.

In accordance with a first arrangement, the target speed reduction ratesetting unit includes: a detection unit that measures a number of timesof operation of the operation unit; and a unit that sets the targetspeed reduction rate in a stepwise manner according to the observednumber of times of operation.

The first arrangement enables the moderate setting of the target speedreduction rate. The stepwise variation in target speed reduction rateenables the driver to change the target speed reduction rate in a widerange by an operation that requires only a relatively short time period.This arrangement thus ensures the excellent operatability.

In accordance with a second arrangement, the target speed reductionsetting unit includes: a detection unit that measures an operation timeof the operation unit; and a unit that sets the target speed reductionrate according to the observed operation time.

In the second arrangement, the target speed reduction rate may be variedrelative to the operation time in a stepwise manner or alternatively ina continuous manner. In the latter case, the target speed reduction ratemay be varied proportional to the operation time or non-linearlyrelative to the operation time. In one example, the target speedreduction rate may be varied relatively gently at the beginning of theoperation and be quickly changed after elapse of a preset time period.

In any case, the target speed reduction rate setting unit of the secondarrangement enables the target speed reduction rate to be set by oneaction, thereby ensuring the excellent operatability. The structure ofcontinuously varying the target speed reduction rate according to theoperation time ensures the minute setting of the target speed reductionrate reflecting the requirement of the driver.

In accordance with a third arrangement, the target speed reductionsetting unit includes: a detection unit that measures a quantity ofoperation of the operation unit; and a unit that sets the target speedreduction rate according to the observed quantity of operation.

In the third arrangement, the target speed reduction rate may be variedrelative to the quantity of operation in a stepwise manner oralternatively in a continuous manner. In any case, the target speedreduction rate setting unit of the third arrangement enables the driverto intuitively recognize the relationship between the operation and thespeed reduction rate. The first through the third arrangements discussedabove may be applied alone or in combination.

In accordance with one preferable application of the present invention,the first vehicle further includes: a switch that gives an instructionto execute braking with the specified speed reduction rate in responseto a predetermined operation by the driver of the vehicle;

and a permission unit that allows operations of all the target speedreduction rate setting unit, the selection unit, the motor driving statespecification unit, and the control unit only in the case where thebraking execution instruction is given by means of the switch. In thevehicle of this application, the operation of the switch switches on andoff the braking control with the specified speed reduction rate, thatis, the currently set target speed reduction rate. When the switch is inON position, the braking control is executed with the speed reductionrate specified by the driver. When the switch is in OFF position, on theother hand, braking is carried out with a predetermined speed reductionrate, irrespective of the specification of the speed reduction rate.This arrangement enables the driver to be clearly conscious of theexecution of the braking control with the speed reduction ratecorresponding to the desired setting of the driver. The driver can thuscontinue driving without feeling any incompatibility by the power sourcebraking.

A diversity of structures may be applied for the switch.

In accordance with one embodiment, the vehicle further includes achangeover unit that changes over a selectable gear ratio range for thetarget gear ratio in response to a predetermined operation by the driverof the vehicle. In this structure, the switch has a mechanism that givesthe braking execution instruction in response to another operation ofthe changeover unit that is different from the predetermined operationfor the changeover.

This arrangement enables the on-off instruction regarding the executionof the braking control with the specified speed reduction rate to begiven without unnecessarily providing any additional switch or relatedelement in the vehicle. The changeover unit is generally disposed in alocation that ensures the easy access of the driver. This arrangementthus ensures the excellent on-off operatability of the switch. Theswitch shares the structure with the conventionally provided changeoverunit. The driver can thus carry out the switch operations withoutfeeling any remarkable incompatibility.

In the case where a gearshift lever is applied for the changeover unit,for example, the switch-on and -off operations may be carried out byoperating the gearshift lever in a movable area, which is different froma conventional movable area to changeover the available range of thechange-speed gear. In accordance with one concrete structure, when agearshift lever, which is slid along a predetermined groove tochangeover the available range of the change-speed gear, is used for thechangeover unit, the gearshift lever is moved in a direction crossingthe predetermined groove, so as to set the switch in ON position or inOFF position. The switch may share the structure with the operation unitfor setting the speed reduction rate. In this case, one applicabledesign causes the switch to be set in ON position by moving thegearshift lever to a specific position where the gearshift leverfunctions as the operation unit discussed above. This arrangementactualizes the switch that has the excellent operatability and makes thedriver feel lesser incompatible, while ensuring the setting of thetarget speed reduction rate.

In accordance with another preferable application of the first vehicleof the present invention, the target speed reduction rate setting unitincludes: a decision unit that determines whether the operation of theoperation unit is valid or invalid; and a prohibition unit thatprohibits the setting of the target speed reduction rate from beingchanged when it is determined that the operation is invalid.

The vehicle of this arrangement effectively prevents the setting of thetarget speed reduction rate from being changed by a wrong, unintentionaloperation of the driver. This arrangement thus prevents the brakingcontrol against the requirement of the driver and improves thecontrollability and the driving stability of the first vehicle of thepresent invention. This prohibition unit is especially effective in thecase where the operation unit for changing the setting of the speedreduction rate is provided on a specific part that allows anunintentional touch of the driver, for example, on a steering wheel.

A variety of modifications may be applied for this arrangement.

In accordance with one embodiment, in the case where the operation unithas a mechanism that allows the driver to give an instruction toincrease the speed reduction rate simultaneously with an instruction todecrease the speed reduction rate, the decision unit determines that theoperation of the operation unit is invalid in the case where theincrease instruction is given simultaneously with the decreaseinstruction.

In the vehicle with the switch for giving the instruction to executebraking with the specified speed reduction rate as discussed above, thedecision unit may determine that the operation of the operation unit isinvalid when the switch is in OFF position.

In the first vehicle of the present invention, the operation unit mayset the speed reduction rate as an absolute value.

It is, however, preferable that the operation unit has a mechanism thatgives an instruction to vary the speed reduction rate, and the targetspeed reduction rate setting unit varies the speed reduction raterelative to a preset initial speed reduction rate as a standard level,in response to the operation of the operation unit, thereby setting thetarget speed reduction rate.

This arrangement enables the driver to regulate the speed reduction rateas an addition to or a subtraction from the initial speed reductionrate, and thereby facilitates the setting of the adequate target speedreduction rate. In the structure of setting the speed reduction rate asan absolute value, it is difficult for the driver to select anappropriate numeral at the beginning. There is accordingly a possibilitythat the specified speed reduction rate is extremely low or high. Thearrangement of regulating the speed reduction rate as an addition to ora subtraction from the initial speed reduction rate, on the other hand,effectively prevents the specified speed reduction rate from beingextremely low or high against the requirement of the driver.

In this arrangement, a variety of settings may be applied for theinitial speed reduction rate.

In the case where the first vehicle further includes: a switch thatgives an instruction to execute braking with the specified speedreduction rate in response to a predetermined operation by the driver ofthe vehicle; a permission unit that allows operations of all the targetspeed reduction rate setting unit, the selection unit, the motor drivingstate specification unit, and the control unit in the case where thebraking execution instruction is given; and an ordinary braking unitthat carries out braking with a predetermined speed reduction rate,irrespective of the operation of the operation unit, in the case wherethe braking execution instruction is not given, the initial speedreduction rate may be set equal to the predetermined speed reductionrate employed by the ordinary braking unit.

This arrangement enables the driver to regulate the speed reduction raterelative to, as the standard, the predetermined speed reduction rateemployed in the process of ordinary braking. The driver can thusintuitively understand the relationship between the current setting andthe actual speed reduction rate and thus readily set the adequate speedreduction rate. At the time point when the braking control with thespecified speed reduction rate is switched on by the operation of theswitch, the speed reduction rate is equal to the initial speed reductionrate, that is, the predetermined speed reduction rate employed in theprocess of ordinary braking. This effectively prevents the driver fromfeeling any shock due to the switch on-off operations. The vehicle ofthis arrangement ensures the on-off of the braking control with thespecified speed reduction rate without making the driver and anypassenger feel incompatible, and thereby attains a smooth drive.

The vehicle of the above arrangement may run while the switch is kept inON position, that is, while the braking control with the currently settarget speed reduction rate is kept on. Since the initial speedreduction rate is equal to the predetermined speed reduction rateemployed in the process of ordinary braking, the driver can drive thevehicle with the switch kept in ON position without feeling anyincompatibility. When the driver needs to adjust the speed reductionrate, this arrangement enables the speed reduction rate to be regulatedquickly without the on operation of the switch.

In the vehicle having the above structure, the initial speed reductionrate may be set to be significantly greater than the predetermined speedreduction rate employed by the ordinary braking unit.

The driver generally feels the necessity of the adjustment of the speedreduction rate in the case where there is an insufficient speedreduction rate in the process of ordinary braking. The arrangement ofsetting the initial speed reduction rate to be significantly greaterthan the predetermined speed reduction rate employed in the process ofordinary braking enables the speed reduction rate desired by the driverto be attained quickly. An appropriate value, which has been determinedaccording to the type of the vehicle, for example, based on experiments,may be set to the supplement of the predetermined speed reduction rate.Alternatively the driver may set a desired value reflecting the ownfeeling to the supplement by a predetermined operation.

In the structure that enables the speed reduction rate to be setrelative to the predetermined initial speed reduction rate as thestandard, it is preferable, that the target speed reduction rate settingunit includes: a cancellation decision unit that determines whether ornot the target speed reduction rate is to be cancelled; and a settingcancellation unit that resets the target speed reduction rate to theinitial speed reduction rate when it is determined that the target speedreduction rate is to be cancelled.

In the vehicle of this arrangement, the setting cancellation unitenables the setting of the target speed reduction rate to be readilyreturned to the initial speed reduction rate. For example, when thedriver repeatedly carries out the operation for setting the target speedreduction rate and makes the current setting unclear, this arrangementenables the setting of the target speed reduction rate to be started allover again relative to the initial value as the standard. In the eventthat a value significantly deviating from the initial speed reductionrate is set to the target speed reduction rate, this arrangement enablesthe target speed reduction rate to be returned to the initial valuequickly and readily, thereby ensuring the excellent controllability.

A variety of structures may be applied for the cancellation decisionunit.

In accordance with one embodiment, when the first vehicle furtherincludes a switch that gives an instruction to execute braking with thespecified speed reduction rate in response to a predetermined operationby the driver of the vehicle, the cancellation decision unit determinesthat the target speed reduction rate is to be cancelled in response toan operation of the switch.

The setting may be cancelled when the position of the switch is changedfrom ON to OFF or vice versa, that is, from OFF to ON.

The driver often forgets the previous setting of the target speedreduction rate after a long time period has elapsed since the previoussetting. Under such circumstances, if the braking control with thepreviously set target speed reduction rate is carried out in response tothe on operation of the switch, there is a fair possibility that thebraking control is carried out with the speed reduction rate unexpectedby the driver. The above arrangement causes the target speed reductionrate to be returned to the initial value every time the switch is set inON position. This effectively prevents the braking control against therequirement of the driver and thus ensures a drive of excellent drivingstability without making the driver feel incompatible.

In accordance with another embodiment, when the first vehicle furtherincludes a failure detection unit that detects a failure of theoperation unit, the cancellation decision unit determines that thetarget speed reduction rate is to be cancelled in response to detectionof the failure.

The arrangement of validating the setting of the target speed reductionrate under the failure condition may lead to the setting of an extremelyhigh value or low value to the target speed reduction rate. The vehicleof the above arrangement effectively eliminates such possibility andensures a drive of excellent driving stability without making the driverfeel incompatible.

In accordance with still another preferable application of the firstvehicle of the present invention, the selection unit selects the targetgear ratio with preference to a preset initial value.

There may be a number of gear ratios that attain the speed reductionrate reflecting the requirement of the driver. The vehicle of the abovearrangement sets the gear ratio with preference to the preset initialvalue. A variety of settings may be applied for the initial value. Forexample, the gear ratio suitable for acceleration following the brakingcontrol may be set to the initial value. In another example, the gearratio that ensures a wide range of practical speed reduction rate may beset to the initial value. The above arrangement provides the vehiclewith characteristics corresponding to the setting of the initial valueand thus improves the controllability and the ride of the vehicle. Thereis generally some latitude in target speed reduction rate specified bythe driver. In the case where the lower limit of the latitude is set tothe target speed reduction rate, there are generally a large number ofgear ratios that attain the target speed reduction rate. The arrangementof setting the gear ratio with preference to the preset initial value isthus especially effective in such cases.

In accordance with one embodiment, when the first vehicle furtherincludes a switch that gives an on-off instruction to execute brakingwith the specified speed reduction rate in response to a predeterminedoperation by the driver of the vehicle, the preset initial value isequal to a previous gear ratio immediately before the braking executioninstruction is given by means of the switch.

This arrangement ensures the braking control with the initial value setequal to the previous gear ratio immediately before the brakingexecution instruction is given by the operation of the switch. Thisprevents the gear ratio of the transmission from being changed inresponse to the on operation of the switch and thus ensures the brakingcontrol with the currently set target speed reduction rate withoutmaking the driver feel incompatible.

In accordance with another preferable application of the presentinvention, the first vehicle further includes an information unit thatinforms the driver of the currently set target speed reduction rate.

The information unit may inform the driver of the target speed reductionrate in the form of a visually recognizable display or in an aurallyrecognizable form. The informed target speed reduction rate may be anabsolute value or a variation from a preset initial value.

When the vehicle includes the switch for giving the instruction toexecute braking with the specified speed reduction rate, it ispreferable that the vehicle has an information unit that informs thedriver of a result of the instruction whether or not to execute thebraking with the specified speed reduction rate.

This arrangement enables the driver to readily check the on-off state ofthe switch and thus effectively prevents wrong operations. Theinformation unit may be a visual display or a sound alarm.

In accordance with still another preferable application of the presentinvention, the first vehicle further includes: a failure detection unitthat detects a failure of the operation unit; and an information unitthat informs the driver of detection of the failure.

The vehicle of this arrangement enables the driver to readily check theoperation unit for a failure. The driver can thus continue drivingwithout feeling any incompatibility even when the operation unit fails.The information unit may be a visual display, a sound alarm, or anyother suitable form. In the vehicle having a display unit that displaysthe currently set speed reduction rate, the detection of a failure maybe displayed in a different form, for example, in a flash, for thepurpose of information.

In accordance with another preferable application of the presentinvention, the first vehicle further includes: a gearshift positioninput unit that inputs a gearshift position, which represents aselectable gear ratio range during a drive of the vehicle; and a storageunit in which speed reduction rates of the vehicle are stored in advancecorresponding to gearshift positions. In this structure, the targetspeed reduction rate setting unit sets the target speed reduction ratein response to the operation of the operation unit and the inputgearshift position by referring to the storage unit. The selection unitselects the target gear ratio that attains the target speed reductionrate with preference to an energy recovery rate in the course ofbraking, irrespective of the gearshift position.

In the vehicle of this arrangement, the gear ratio of the transmissionused in the braking process is set with preference to the energyrecovery rate, irrespective of the selectable gear ratio range specifiedby the gearshift position input unit. In the case where the advantageousgear ratio from the viewpoint of energy recovery is present out of theselectable gear ratio range specified by the driver, the vehicle of theabove arrangement enables the braking control with the advantageous gearratio. This arrangement enhances the energy recovery rate of the vehicleduring the braking control. The energy recovery rate here represents anefficiency of regeneration carried out by the motor to regenerate thekinetic energy of the vehicle.

The vehicle of this arrangement attains the speed reduction ratepreviously set according to the gear ratio range. The driver specifiesthe selectable range of gear ratio, which leads to the braking controlwith the desired speed reduction rate. The gear ratio of thetransmission during a drive of the vehicle is restricted in theselectable gear ratio range specified by the driver. This arrangementenables the vehicle to be quickly accelerated with an accelerationreflecting the requirement of the driver, after the braking control.

The vehicle of this arrangement allows selection of the gear ratio inthe braking process out of the specified selectable gear ratio range,thus attaining the speed reduction and acceleration reflecting therequirement of the driver while enhancing the energy recovery rate ofthe vehicle. This improves the effectiveness of the power source brakingand enhances the controllability of the vehicle.

In the structure of selecting the gear ratio with preference to theenergy recovery rate, it is preferable that the first vehicle furtherincludes: an accumulator unit; and a detection unit that measures aremaining charge of the accumulator unit. In this case, the selectionunit selects the target gear ratio according to the observed remainingcharge of the accumulator unit.

In the case where the accumulator unit has a relatively low remainingcharge, the gear ratio is selected to increase the quantity of electricpower regenerated from the kinetic energy of the vehicle. In the casewhere the accumulator has a relatively high remaining charge, on theother hand, the gear ratio is selected to decrease the quantity ofregenerated electric power. This arrangement advantageously causes theremaining charge of the accumulator unit to be kept in a favorablestate. The selection of the gear ratio with preference to the energyrecovery rate is not synonymous with the selection of the gear ratiothat gives the maximum quantity of regeneration, but means the selectionof the gear ratio that ensures regeneration of an adequate quantity ofenergy according to the driving conditions of the vehicle.

It is also preferable that the selection unit selects the target gearratio in a specific range that prevents an extreme change of drivingcondition of a power source of the vehicle in a transient time frombraking control to another driving state of the vehicle.

In the vehicle of this arrangement, the gear ratio set with preferenceto the energy recovery rate is not selected unconditionally but islimited in a specific range. When the driver specifies the selectablegear ratio range, the gear ratio adopted for a drive following thebraking control is within the selectable gear ratio range. In the casewhere the braking control is carried out with the gear ratio thatsignificantly deviates from the specified gear ratio range, the gearratio of the transmission is drastically changed in a transient timefrom the braking control to another driving state. The drivingconditions of the power source are remarkably varied with the drasticchange of the gear ratio. If the variation is extremely large, sometroubles occur; for example, a significant vibration occurs in thevehicle or the driving state of the power source becomes unstable. Inthe vehicle of the above arrangement, the gear ratio is selected in thespecific range that is set by taking into account the variation. Thisarrangement effectively prevents the occurrence of possible troubles inthe transient time from the braking control to another driving state.

In the vehicle of the above arrangement, it is also preferable that thetransmission attains a plurality of gear ratios set stepwise, and theselection unit selects the target gear ratio by allowing a deviationfrom the selectable gear ratio range corresponding to the inputgearshift position by one step.

The vehicle of this arrangement facilitates the control of thetransmission in the transient time from braking to another drivingstate. As described previously, when the driver specifies the selectablegear ratio range, the gear ratio adopted for a drive subsequent to thebraking control is within the selectable gear ratio range. In the casewhere the braking control is carried out with the gear ratio thatdeviates from the specified gear ratio range by several steps, it isnecessary to change the gear ratio of the transmission over the severalsteps in the transient period from the braking control to anotherdriving state. The control actualizing such a change is undesirablycomplicated, and the change of the gear ratio may require a relativelylong time. In the vehicle of the above arrangement, the selected gearratio does not deviate from the specified gear ratio range by two ormore steps. This arrangement avoids such complicated control and ensuresthe quick change of the gear ratio.

The present invention is also directed to a second vehicle that includesa motor connected with a drive shaft and is braked by means of a torqueoutput from the motor. The second vehicle includes: an operation unit,through an operation of which a driver of the vehicle specifies a speedreduction rate in a process of braking with the motor; a target,speedreduction rate setting unit that sets a target speed reduction rate inresponse to the operation of the operation unit; a motor driving statespecification unit that specifies a target driving state of the motor,in order to enable a braking force that attains the currently set targetspeed reduction rate to be applied to the drive shaft; a control unitthat drives the motor in the specified target driving state; and avariation unit that varies a possible range of setting of the targetspeed reduction rate according to a driving condition of the vehicle.

In the second vehicle of the present invention, the possible range ofsetting of the target speed reduction rate is varied according to thedriving conditions of the vehicle. This arrangement attains the adequatespeed reduction rate according to the driving conditions and therebysignificantly improves the controllability and the driving stability ofhe vehicle.

The possible range of the speed reduction rate, in which the vehicle isstably driven, varies according to the driving state of the vehicle. Byway of example, in the case where the road surface has a very slipperycondition, braking with a higher speed reduction rate than required maycause a slip or a skid of the vehicle. In another example, in the casewhere the traffic is heavy to make the distance between adjacentvehicles on the same traffic lane relatively narrow, braking with alower speed reduction rate than required needs a change of the footposition to the brake pedal, in order to compensate for theinsufficiency of the speed reduction rate. This may significantly damagethe advantage of the power-source braking.

The second vehicle of the present invention changes the possible rangeof setting of the target speed reduction rate according to the drivingconditions of the vehicle and thereby ensures the braking control withthe adequate speed reduction rate corresponding to the current drivingconditions. The second vehicle of the present invention thus enhancesthe driving stability of the vehicle.

Like the first vehicle discussed above, the second vehicle of thepresent invention may be an electric vehicle, a hybrid vehicle, or anyother suitable vehicle.

In accordance with one preferable application of the present invention,the second vehicle further includes: a transmission that enablesselection of a plurality of gear ratios in a process of powertransmission; a selection unit that selects a target gear ratio among aplurality of available gear ratios, the target gear ratio enabling thecurrently set target speed reduction rate to be attained by the torqueof the motor; and a transmission control unit that controls thetransmission to attain the target gear ratio.

The selection unit selects an adequate gear ratio according to the speedreduction rate specified by the driver and the magnitude of the torqueoutput from the motor. Controlling the target torque of the motor at theadequate gear ratio ensures the speed reduction rate required by thedriver. The vehicle of the above arrangement totally controls both thetransmission and the motor, thereby implementing the braking in responseto the specification by the driver in a wide range.

The selection unit and the transmission control unit here represent theunits that respectively carry out selection and control in a wide sense.The selection unit is not restricted to the unit that selects an onlytarget gear ratio. When there are a plurality of gear ratios mapped tothe target speed reduction rate, the selection unit may select anoptimum gear ratio among the plurality of gear ratios or select all theplurality of gear ratios as the target gear ratio. The transmissioncontrol unit may omit the changeover control of the gear ratio in thecase where the selected target gear ratio has already been attained.

As described previously, the technique of the present invention isapplicable to a diversity of vehicles. The technique of the presentinvention is especially preferably applied to the vehicle further havingan engine in a specific state of linkage that enables a power to beoutput to the drive shaft. In this structure, the motor driving statespecification unit sets a target torque of the motor by taking intoaccount a braking torque applied by the engine.

In this structure, it is preferable that the second vehicle has aconnection mechanism that connects and disconnects transmission of powerfrom the engine to the drive shaft. It is more preferable that thesecond vehicle further includes a connection mechanism control unit thatcontrols the connection mechanism to disconnect the transmission ofpower between the engine and the drive shaft in a process of brakingwith the torque of the motor.

The vehicle of the present invention carries out braking with electricpower regenerated by the motor. When the vehicle has an engine, abraking force is added by engine brake. The engine brake causes therotational power of the drive shaft to be consumed by the pumping andthe friction of the engine, so as to implement the braking control. Theengine brake reduces the quantity of regenerated electric powercorresponding to its braking force.

The vehicle of the above arrangement enables the transmission of powerfrom the engine to the drive shaft to be connected and disconnected.Disconnection of the power transmission in the braking process increasesthe quantity of regenerated electric power, and ensures the effectiveuse of the kinetic energy of the vehicle. The connection anddisconnection of the power may be carried out manually. The unit forcontrolling the connection mechanism, however, preferably ensures themore appropriate regeneration of energy.

The connection mechanism of the power has another advantage, that is,regulation of the braking force by the motor and engine brake. While theconnection mechanism is in a connected position to add the braking forcefrom the engine to the drive shaft, the drive shaft receives both thebraking force by the engine brake and the braking force by theregenerative braking with the motor. This gives a large total brakingforce. In the connected position of the connection mechanism, thebraking force by the engine brake is continuously added to raise thelower limit of the total braking force. Setting the connection mechanismin a disconnected position is accordingly desirable when it is requiredto decrease the lower limit of the total braking force.

In the vehicle of the above arrangement, controlling the connectionmechanism regulates the upper limit and the lower limit of the brakingforce applicable to the drive shaft. This ensures the adequate powersource braking. When a large braking force is required, the foot brakingis generally combined with the power source braking. From the viewpointsof energy efficiency and regulation of the lower limit of the powersource braking, it is highly effective to set the connection mechanismin the disconnected position in the braking process. Such control isespecially effective to prevent the occurrence of a slip or a skid asdiscussed later.

The vehicle having the connection mechanism of the power may furtherinclude the transmission, the selection unit, and the transmissioncontrol unit discussed above. In one structure of this case, setting theconnection mechanism in the disconnected position causes the gear ratioto have no effects on the braking control. In other words, any value maybe set to the gear ratio under such conditions. As mentioned previously,the selection unit and the transmission control unit of the presentinvention carry out the selection and the control in a wide sense. Inthe structure that causes the gear ratio to have no effects on thebraking control, the selection unit selects all the gear ratios as thetarget gear ratio. In this case, since the target gear ratio has alreadybeen attained, the transmission control unit always omits the changeovercontrol of the gear ratio.

In the second vehicle of the present invention, a variety of techniquesmay be applied to vary the possible range of setting of the target speedreduction rate. One available technique widens the possible range ofsetting of the target speed reduction rate when the vehicle is in aspecific driving state that ensures the sufficient driving stabilityeven under the condition of varying speed reduction rate in a widerange. Another available technique wholly shifts the possible range ofsetting of the target speed reduction rate. For example, when it isdetermined that the vehicle runs on a down slope, the possible range ofsetting of the target speed reduction rate is wholly shifted in anincreasing direction.

In accordance with one preferable application of the second vehicle ofthe present invention, the variation unit for varying the possible rangeof setting of the target speed reduction rate includes: a decision unitthat determines whether or not a restriction condition to restrict thetarget speed reduction rate is fulfilled; and a restriction unit thatactually restricts the target speed reduction rate when the restrictioncondition is fulfilled.

This application narrows the possible range of setting of the targetspeed reduction rate.

The vehicle of the above arrangement effectively prevents the driverfrom setting an excessively large or small speed reduction rate thanrequired, thereby improving the driving stability of the vehicle. Therange of the speed reduction rate that ensures the sufficient drivingstability of the vehicle often depends upon the driving state of thevehicle. In the vehicle of the above arrangement, the possible range ofsetting of the target speed reduction rate is varied flexibly andappropriately according to the driving state of the vehicle. Thepossible range of setting of the target speed reduction rate may benarrowed by lowering the upper limit or alternatively by raising thelower limit. Any appropriate method should be adopted according to thedriving state of the vehicle.

In the second vehicle of the present invention, a variety of techniquesare applicable to determine whether or not the target speed reductionrate is to be restricted.

In accordance with a first embodiment, the decision unit determines thatthe restriction condition is fulfilled when there is a slip occurring indriving wheels connected with the drive shaft.

Braking with a high speed reduction rate on a road surface having arelatively low friction coefficient, for example, the snow-covered roador the wet road, may cause a slip or a skid of the vehicle. A slip or askid of the driving wheels may be set to the restriction condition. Thisprevents the occurrence of a slip or a skid and improves the drivingstability of the vehicle.

The occurrence of a slip or a skid may be detected by a variety ofmethods. One available method measures the numbers of rotations ofplural driving wheels and determines the occurrence of a slip or a skidwhen there is a difference of or over a preset level between theobserved numbers of rotations of the respective driving wheels. Thesecond vehicle of the present invention has the motor connected with thedrive shaft, so that the occurrence of a slip or a skid may bedetermined by variations of the torque and the revolving speed of themotor. In a vehicle with an acceleration sensor mounted thereon, theoccurrence of a slip or a skid may be determined, based on the output ofthe acceleration sensor. The determination of the occurrence of a slipor a skid may be carried out not only at the time of braking but at thetime of ordinary driving.

In accordance with a second embodiment, the decision unit carries outthe determination, based on an operation of a switch that gives aninstruction to restrict the possible range of setting of the targetspeed reduction rate.

In the vehicle of the above configuration, the driver intentionallyoperates the switch to restrict the possible range of setting of thetarget speed reduction rate. For example, when determining that the roadsurface has a relatively low friction coefficient, the driver operatesthe switch to prevent the possible occurrence of a slip or a skid. Thisarrangement thus further improves the driving stability of the vehicle.The switch here is different from the operation unit, through anoperation of which the driver specifies the speed reduction rate. Theoperation of the switch enables the driver to change the setting of thespeed reduction rate without a fear of the occurrence of a slip or askid.

The switch here is not restricted to the above switch that is operatedwhen the driver determines that the road surface has a relatively lowfriction coefficient. Other switches may be provided for a variety ofpurposes. The target speed reduction rate may be restricted in responseto ON position of the switch or alternatively in response to OFFposition of the switch. The target speed reduction rate may berestricted in a stepwise manner in response to the operation of theswitch.

The restriction of the target speed reduction rate may be carried outunder a variety of conditions. For example, in a vehicle having aspecific sensor that measures the distances from adjacent vehicles onthe same traffic lane, the target speed reduction rate is restricted,based on the distance of or below a predetermined level set as therestriction condition. In another example, in a vehicle having aspecific apparatus that verifies the position of the vehicle intopography, the target speed reduction rate is restricted according tothe variation in height of the road, on which the vehicle runs.

A variety of methods are applicable to restrict the target speedreduction rate. One method wholly restricts the variation of the targetspeed reduction rate relative to each quantity of operation of theoperation unit for specifying the speed reduction rate. This arrangementleads to a gentler variation of the target speed reduction rate per unitquantity of operation of the operation unit.

In accordance with another preferable embodiment, the restriction unitrestricts the target speed reduction rate to be not higher than apredetermined upper limit.

This arrangement advantageously facilitates the restriction of thetarget speed reduction rate. The variation of the target speed reductionrate per unit quantity of operation of the operation unit is fixed,irrespective of restriction or non-restriction of the target speedreduction rate. The driver can thus readily set the desired speedreduction rate.

In accordance with still another preferable embodiment, the restrictionunit carries out feedback control to restrict the target speed reductionrate until the restriction condition becomes unfulfilled.

This arrangement restricts the target speed reduction rate to a specificrange where the restriction condition is not fulfilled, thus furtherimproving the driving stability of the vehicle. This arrangement doesnot reduce the speed reduction rate unnecessarily. For example, it isassumed that the occurrence of a slip or a skid of the driving wheels isset to the condition for restricting the target speed reduction rate.The speed reduction rate that prevents the occurrence of a slip or askid depends upon the friction coefficient of the road surface. In thevehicle that carries out the restriction through the feedback control,the target speed reduction rate is gradually lowered until no occurrenceof a slip or a skid is assured. This arrangement effectively preventsthe occurrence of a slip or a skid without reducing the target speedreduction rate unnecessarily.

Although the above description regards the case of restricting thetarget speed reduction rate, any of the above applications may beadopted in the vehicle having a unit of extending the target speedreduction rate.

In accordance with another preferable application of the presentinvention, the second vehicle further includes an information unit thatinforms the driver of a variation in possible range of setting of thetarget speed reduction rate.

This arrangement enables the driver to drive the vehicle without feelingany incompatibility. The information unit may inform the driver of thewidened range of setting of the target speed reduction rate or thenarrowed range of setting of the target speed reduction rate. In theformer case, the driver recognizes that the speed reduction rate may beset in a wider range, and drives the vehicle with a desired speedreduction rate. In the latter case, the driver is informed of thepossibility that the specified speed reduction rate is not attained.This arrangement favorably reduces the incompatible feeling of thedriver and the fear of a possible failure in the braking process.

The information unit may be a visual display or a sound alarm. In thevehicle having a display unit that displays the speed reduction rate setby the driver, the varied range of the target speed reduction rate maybe displayed in a different form, for example, in a flash, for thepurpose of information.

In any of the vehicles with the transmission discussed above, thefollowing procedure may be applied to set and regulate the gear ratio.

The motor and the torque may be designed to have a plurality ofcombinations that attain a predetermined speed reduction rate at apreset vehicle speed, among a variety of combinations of the torque ofthe power source and the gear ratio of the transmission. Namely thereare a plurality of combinations that attain the predetermined targetspeed reduction rate at the preset vehicle speed. This arrangementensures the braking control with an optimum combination according to thedriving state of the vehicle, and accordingly allows the braking withthe motor to be utilized in a wide range of driving conditions.

In the case where both the motor and the engine can be utilized forbraking, it is desirable that the plurality of combinations includethose corresponding to the regenerative operation of the motor and thosecorresponding to the power operation of the motor.

When the vehicle has an engine as the power source, the braking controlmay be carried out with the torques of both the motor and the engine.According to the gear ratio, the braking torque of the engine may beinsufficient or excess to the desired speed reduction rate. In theformer case, the motor performs the regenerative operation to supplementthe insufficiency of the speed reduction rate, so as to implement thedesired braking control. In the latter case, the motor performs thepower operation to ensure the braking control with the desired speedreduction rate. Even when a relatively small gear ratio is adopted for adrive, the braking control with the motor carrying out the regenerativeoperation enables the desired speed reduction rate to be attainedwithout the changeover of the gear ratio, thus ensuring a smooth drive.The braking control with the motor carrying out the power operationduring a drive, on the other hand, advantageously enables the quickacceleration subsequent to the deceleration.

In the above structure, the selection of the gear ratio is carried out,for example, based on the remaining charge of the accumulator unit. Itis here assumed that there are a plurality of target gear ratios. Oneexemplified procedure selects a gear ratio corresponding to the poweroperation of the motor in the case where the remaining charge is notless than a predetermined level, while otherwise selecting a gear ratiocorresponding to the regenerative operation of the motor. Thisarrangement enables the braking control to be carried out with thecombination corresponding to the power operation of the motor, when theaccumulator unit has the remaining charge close to its full chargelevel. The vehicle of such arrangement thus carries out the brakingcontrol with the motor, irrespective of the charge level of theaccumulator unit.

The technique of the present invention is also actualized by a method ofcontrolling operation of any of the vehicles discussed above.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 schematically illustrates the structure of a hybrid vehicle inone embodiment according to the present invention;

FIG. 2 illustrates the internal structure of a transmission 100;

FIG. 3 shows the relationship between the state of engagement of therespective clutches, brakes, and one-way clutches and the position ofthe change-speed gear;

FIG. 4 shows an operation unit 160 for selecting the gearshift positionin the hybrid vehicle of the embodiment;

FIG. 5 shows operation elements mounted on a steering wheel;

FIG. 6 shows another operation unit 160A having a modified structure;

FIG. 7 shows an instrument panel in the hybrid vehicle of theembodiment;

FIG. 8 shows connections of input and output signals into and from acontrol unit 70 in the hybrid vehicle of the embodiment;

FIG. 9 is a map showing the relationship between the driving state ofthe vehicle and the power source;

FIG. 10 is a map showing the relationship between the position of thechange-speed gear in the transmission 100 and the driving state of thevehicle;

FIG. 11 is a map showing the combinations of the vehicle speed, thedeceleration, and the position of the change-speed gear in the hybridvehicle of the embodiment;

FIG. 12 is a map showing the relationship between the deceleration andthe position of the change-speed gear at a certain vehicle speed Vs;

FIG. 13 is a graph showing a variation in deceleration at a fixedposition of the change-speed gear;

FIG. 14 schematically illustrates a comparison between a braking torquein the case where the motor 20 carries out the regenerative operationand a braking torque in the case where the motor 20 carries out thepower operation;

FIG. 15 is a flowchart showing a speed reduction control routine;

FIG. 16 is a flowchart showing a routine of the initial setting process;

FIG. 17 is a flowchart showing a routine of the deceleration settingprocess;

FIG. 18 is a flowchart showing a routine of the deceleration restrictingprocess;

FIG. 19 is a timing chart showing a first example of the setting of thedeceleration;

FIG. 20 is a timing chart showing a second example of the setting of thedeceleration;

FIG. 21 is a timing chart showing a third example of the setting of thedeceleration;

FIG. 22 is a timing chart showing a fourth example of the setting of thedeceleration;

FIG. 23 is a flowchart showing a change-speed gear position selectionroutine;

FIG. 24 is a flowchart showing another routine of the decelerationrestricting process as one modification;

FIG. 25 is a graph showing another process of restricting thedeceleration;

FIG. 26 is a modified example of the map showing the combinations of thevehicle speed, the deceleration, and the position of the change-speedgear;

FIG. 27 shows the revolving speed of the power source, the engine brake,and the regenerative torque at the respective positions of thechange-speed gear to attain a deceleration shown by an area A in FIG.26;

FIG. 28 is a flowchart showing another change-speed gear positionselection routine executed in this modified example;

FIG. 29 illustrates the structure of a series hybrid vehicle;

FIG. 30 shows an operation unit 160 for selecting the gearshift positionin a hybrid vehicle of a second embodiment according to the presentinvention;

FIG. 31 is a graph showing a variable range of the deceleration at eachposition of the change-speed gear in the hybrid vehicle of the secondembodiment;

FIG. 32 is a flowchart showing a drive control routine executed in thesecond embodiment;

FIG. 33 is a flowchart showing a routine of the change-speed gearposition setting process executed in the second embodiment;

FIG. 34 is a flow chart showing a routine of the deceleration settingprocess executed in the second embodiment;

FIG. 35 is a flowchart showing a routine of the change-speed gearposition changeover process executed in the second embodiment;

FIG. 36 shows the relationship between the setting of the decelerationand the changeover of the change-speed gear position as an example;

FIG. 37 is a flowchart showing a routine of the change-speed gearposition changeover process executed in a first modification of thesecond embodiment;

FIG. 38 shows the settings of the deceleration in a second modificationof the second embodiment;

FIG. 39 shows the settings of the deceleration in a third modificationof the second embodiment;

FIG. 40 shows the settings of the deceleration using a slide knob 161 ina fourth modification of the second embodiment;

FIG. 41 shows the settings of the deceleration by operating the slideknob 161 in an increasing direction;

FIG. 42 schematically illustrates the structure of another hybridvehicle in a third embodiment according to the present invention;

FIG. 43 is a flowchart showing a speed reduction control routineexecuted in the third embodiment; and

FIG. 44 schematically illustrates the structure of a vehicle in a fourthembodiment according to the present invention.

BEST MODES OF CARRYING OUT THE INVENTION

Embodiments of the present invention are explained as:

A. First Embodiment

A1. Structure of Apparatus

A2. Generation Operations

A3. Drive Control Process

A4. First Modification of First Embodiment

A5. Second Modification of First Embodiment

A6. Third Modification of First Embodiment

B. Second Embodiment

B1. Structure of Apparatus

B2. Drive Control Process

B3. First Modification of Second Embodiment

B4. Second Modification of Second Embodiment

B5. Third Modification of Second Embodiment

B6. Fourth Modification of Second Embodiment

C. Third Embodiment

D. Fourth Embodiment

E. Other Modifications

The embodiments are discussed below in detail in the above order.

A. First Embodiment

A1. Structure of Apparatus

FIG. 1 schematically illustrates the structure of a hybrid vehicle inone embodiment according to the present invention. The hybrid vehicle ofthe embodiment has an engine 10 and a motor 20 as the power sourcethereof. A power system of the hybrid vehicle of this embodimentincludes the engine 10, the motor 20, a torque converter 30, and atransmission 100 that are connected in series. More specifically, themotor 20 is linked with a crankshaft 12 of the engine 10, whereas arotating shaft 13 of the motor 20 is linked with the torque converter30. An output shaft 14 of the torque converter 30 is linked with thetransmission 100. An output shaft 15 of the transmission 100 is linkedwith an axle 17 via a differential gear 16. A left driving wheel 18L anda right driving wheel 18R are attached to the axle 17.

The engine 10 is an ordinary gasoline engine. The engine 10 has amechanism of regulating the open and close timings of an intake valve,which causes a gaseous mixture of gasoline and the air to be sucked intoa cylinder, and an exhaust valve, which causes the hot combustionexhaust to be discharged from the cylinder, relative to verticalmovements of a piston (hereinafter this mechanism is referred to as theVVT mechanism). The structure of the VVT mechanism is known in the artand is thus not described here in detail. The VVT mechanism regulatesthe open and close timings of the intake and exhaust valves to delay theactual closing operations of the respective valves relative to thevertical movements of the piston, thereby reducing the pumping loss ofthe engine 10. This results in decreasing the braking force by enginebrake. The VVT mechanism also reduces the torque to be output from themotor 20 in the course of motoring the engine 10. The VVT mechanismcontrols the open and close timings of the respective valves to attainthe highest combustion efficiency according to the speed of the engine10 in the process of outputting power through combustion of gasoline.

The motor 20 is a three-phase synchronous motor, which includes a rotor22 with a plurality of permanent magnets attached on the circumferentialface thereof and a stator 24 with three-phase coils wound thereon togenerate a revolving magnetic field. The motor 20 is driven to rotate bythe interaction between the magnetic field generated by the permanentmagnets attached to the rotor 22 and the magnetic field generated by thethree-phase coils wound on the stator 24. When the rotor 22 is rotatedby an external force, the interaction between these magnetic fieldscauses an electromotive force between both ends of the three-phasecoils. A sine wave polarized motor, in which the magnetic flux densitybetween the rotor 22 and the stator 24 is distributed in the form of asine function in the circumferential direction, is applicable for themotor 20. A non-sine wave polarized motor that can output a relativelylarge torque is, however, applied for the motor 20 in this embodiment.

The stator 24 is electrically connected to a battery 50 via a drivingcircuit 40. The driving circuit 40 is constructed as a transistorinverter that: includes a plural pairs of transistors, one as a sourceand the other as a sink, provided respectively for the three phases ofthe motor 20. As described in FIG. 1, the driving circuit 40 iselectrically connected with a control unit 70. The control unit 70carries out PWM (pulse width modulation) control of the on- and off-timeof the respective transistors included in the driving circuit 40. ThePWM control causes quasi three-phase alternating currents to be outputfrom the battery 50 as the power source and flow through the three-phasecoils of the stator 24, so as to generate a revolving magnetic field.The motor 20 functions either as a motor or a generator by means of therevolving magnetic field.

The torque converter 30 is a known power transmission mechanism bytaking advantage of a fluid. The input shaft of the torque converter 30,that is, the output shaft 13 of the motor 20, is not mechanically linkedwith the output shaft 14 of the torque converter 30, so that the inputand output shafts 13 and 14 of the torque converter 30 are rotatable inthe presence of a slide. A turbine with a plurality of blades isattached respectively to the input and output shafts 13 and 14 of thetorque converter 30. The turbines set on the input and output shafts 13and 14 are arranged to face each other in the torque converter 30. Thetorque converter 30 has a sealed structure that is filled withtransmission oil. The transmission oil works on the respective turbines,so that power is transmitted from one rotating shaft to the otherrotating shaft. Since these rotating shafts are rotatable in thepresence of a slide, the power input from one rotating shaft isconverted to a different combination of revolving speed and torque andtransmitted to the other rotating shaft.

The transmission 100 includes a plurality of gear units, clutches,one-way clutches, and brakes and changes the gear ratio, so as to enablethe power input from the output shaft 14 of the torque converter 30 tobe converted to a different combination of torque and revolving speedand transmitted to the output shaft 15 of the transmission 100. FIG. 2shows the internal structure of the transmission 100. The transmission100 of this embodiment mainly includes an auxiliary transmission unit110 (a portion on the left side of the dotted line in FIG. 2) and aprimary transmission unit 120 (a portion on the right side of the dottedline). The structure ensures five forward speeds and one reverse speed.

The detailed structure of the transmission 100 is described sequentiallyfrom the rotating shaft 14. As illustrated in FIG. 2, the auxiliarytransmission unit 110 constructed as an overdrive unit converts thepower input from the rotating shaft 14 at a predetermined gear ratio andtransmits the converted power to a rotating shaft 119. The auxiliarytransmission unit 110 includes a first planetary gear unit 112 of asingle pinion type, a clutch C0, a one-way clutch F0, and a brake B0.The first planetary gear unit 112 includes three different gears, thatis, a sun gear 114 revolving on the center, a planetary pinion gear 115revolving both round the sun gear 114 and on its axis, and a ring gear118 revolving round the planetary pinion gear 115. The planetary piniongear 115 is supported on a rotating part called a planetary carrier 116.

In the planetary gear unit, when the rotating conditions of two gearsselected among the three gears are determined, the rotating condition ofthe residual gear is automatically determined. The rotating conditionsof the respective gears in the planetary gear unit are expressed byEquations (1) known in the field of mechanics and given below:

Ns=(1+ρ)/ρ×Nc−Nr/ρ

Nc=ρ/(1+ρ)×Ns+Nr/(1+ρ)

Nr=(1+ρ)Nc−ρNs

 Ts=Tc×ρ/(1+ρ)=ρTr

Tr=Tc/(1+ρ)  (1)

where ρ denotes the number of teeth in the sun gear to the number ofteeth in the ring gear, Ns represents the revolving speed of the sungear, Ts represents the torque of the sun gear, Nc represents therevolving speed of the planetary carrier, Tc represents the torque ofthe planetary carrier, Nr represents the revolving speed of the ringgear, and Tr represents the torque of the ring gear.

In the auxiliary transmission unit 110, the rotating shaft or the outputshaft 14 of the torque converter 30, which corresponds to the inputshaft of the transmission 100, is linked with the planetary carrier 116.The one-way clutch F0 and the clutch C0 are disposed in parallel betweenthe planetary carrier 116 and the sun gear 114. The one-way clutch F0 isset in a specific direction that engages when the sun gear 114 hasnormal rotations relative to the planetary carrier 116, that is, whenthe sun gear 114 rotates in the same direction as that of the inputshaft 14 of the transmission 100. The sun gear 114 is connected to themultiple disc brake B0 that can stop the rotation of the sun gear 114.The ring gear 118 corresponding to the output of the auxiliarytransmission unit 110 is linked with the rotating shaft 119, whichcorresponds to the input shaft of the primary transmission unit 120.

In the auxiliary transmission unit 110 of the above configuration, theplanetary carrier 116 integrally rotates with the sun gear 114 in thestate of engagement of either the clutch C0 or the one-way clutch F0.According to Equations (1) given previously, when the sun gear 114 andthe planetary carrier 116 have an identical revolving speed, therevolving speed of the ring gear 118 is also equal to the identicalrevolving speed. In this state, the revolving speed of the rotatingshaft 119 is identical with the revolving speed of the input shaft 14.In the state of engagement of the brake B0 to stop the rotation of thesun gear 114, on the other hand, according to Equations (1),substitution of the value ‘0’ into the revolving speed Ns of the sungear 114 makes the revolving speed Nr of the ring gear 118 higher thanthe revolving speed Nc of the planetary carrier 116. Namely the rotationof the rotating shaft 14 is accelerated and subsequently transmitted tothe rotating shaft 119. The auxiliary transmission unit 110 selectivelyperforms the function of directly transmitting the power input from therotating shaft 14 to the rotating shaft 119 and the function ofaccelerating the input power and then transmitting the accelerated powerto the rotating shaft 119.

The primary transmission unit 120 includes three planetary gear units130, 140, and 150, two clutches C1 and C2, two one-way clutches F1 andF2, and four brakes B1 through B4. Like the first planetary gear unit112 included in the auxiliary transmission unit 110, each of theplanetary gear units 130, 140, and 150 includes a sun gear, a planetarycarrier, a planetary pinion gear, and a ring gear. The three planetarygear units 130, 140, and 150 are linked as discussed below.

A sun gear 132 of the second planetary gear unit 130 is integrallylinked with a sun gear 142 of the third planetary gear unit 140. Thesesun gears 132 and 142 may be connected with the input shaft 119 via theclutch C2. The rotating shaft with these sun gears 132 and 142 isconnected with the brake B1 to stop the rotation of the rotating shaft.The one-way clutch F1 is set in a specific direction that engages in thecase of reverse rotation of this rotating shaft. The brake B2 is alsoconnected with this rotating shaft to stop the rotation of the one-wayclutch F1.

A planetary carrier 134 of the second planetary gear unit 130 isconnected with the brake B3 to stop the rotation of the planetarycarrier 134. A ring gear 136 of the second planetary gear unit 130 isintegrally linked with a planetary carrier 144 of the third planetarygear unit 140 and a planetary carrier 154 of the fourth planetary gearunit 150. The ring gear 136 and the planetary carriers 144 and 154 arefurther connected with the output shaft 15 of the transmission 100.

A ring gear 146 of the third planetary gear unit 140 is linked with asun gear 152 of the fourth planetary gear unit 150 and with a rotatingshaft 122. The rotating shaft 122 may be linked with the input shaft 119of the primary transmission unit 120 via the clutch C1. A ring gear 156of the fourth planetary gear unit 150 is connected with the brake B4 tostop the rotation of the ring gear 156 and with the one-way clutch F2that is set to engage in the state of reverse rotation of the ring gear156.

The clutches C0 through C2 and the brakes B0 through B4 mounted on thetransmission 100 engage and disengage by means of the hydraulicpressure. The respective clutches and brakes are connected with pipingof hydraulic pressure and elements including solenoid valves forregulating the hydraulic pressure, although these constituents are notspecifically illustrated. In the hybrid vehicle of the embodiment, thecontrol unit 70 outputs control signals to these solenoid valves andother related elements, so as to control the operation of the respectiveclutches and brakes.

The transmission 100 of the embodiment can set the change-speed gear ata position selected among five forward speeds and one reverse speedthrough the combination of engagement and disengagement of the clutchesC0 through C2 and the brakes B0 through B4. The transmission 100 alsohas a Neutral position and a Parking position. FIG. 3 shows therelationship between the state of engagement of the respective clutches,brakes, and one-way clutches and the position of the change-speed gear.In the table of FIG. 3, the circle represents a normal state ofengagement, the double circle represents an engagement in the case ofpower-source braking, and the triangle represents a specific state ofengagement that is not involved in the transmission of power. Thepower-source braking here implies the braking by means of the engine 10and the motor 20. The engagement of the one-way clutches F0 through F2is not based on the control signal of the control unit 70 but is basedon the direction of rotation of each corresponding gear.

As shown in FIG. 3, in the case of either a Parking (P) position or aNeutral (N) position, the clutch C0 and the one-way clutch F0 engage.Since both the clutches C2 and C1 disengage, the power is nottransmitted from the input shaft 119 of the primary transmission unit120 to the downstream elements.

In the case of the first speed (1^(st)), the clutches C0 and C1 and theon-way clutches F0 and F2 engage. Under the application of engine brake,the brake B4 further engages. This is equivalent to the state where theinput shaft 14 of the transmission 100 is directly linked with the sungear 152 of the fourth planetary gear unit 150. The power is accordinglytransmitted to the output shaft 15 at a certain gear ratio correspondingto the gear ratio of the fourth planetary gear unit 150. The ring gear156 is restricted not to rotate reversely by the function of the one-wayclutch F2. The revolving speed of the ring gear 156 is thus practicallyequal to zero. Under such conditions, according to Equations (1) givenpreviously, the relations between a revolving speed Nin and a torque Tinof the input shaft 14 and a revolving speed Nout and a torque Tout ofthe output shaft 15 are expressed by Equations (2) given below:

Nout=Nin/k 1

 Tout=k 1×Tin

k 1=(1+ρ4)/ρ4  (2)

where ρ4 denotes the gear ratio of the fourth planetary gear unit 150.

In the case of the second speed (2^(nd)), the clutch C1, the brake B3,and the one-way clutch F0 engage. Under the application of engine brake,the clutch C0 further engages. This is equivalent to the state where theinput shaft 14 of the transmission 100 is directly linked with the sungear 152 of the fourth planetary gear unit 150 and with the ring gear146 of the third planetary gear unit 140. In this state, the planetarycarrier 134 of the second planetary gear unit 130 is fixed. The sun gear132 of the second planetary gear unit 130 and the sun gear 142 of thethird planetary gear unit 140 have an identical revolving speed. Thering gear 136 and the planetary carrier 144 have an identical revolvingspeed. Under such conditions, according to: Equations (1) givenpreviously, the rotating conditions of the second and third planetarygear units 130 and 140 are determined unequivocally. The relationsbetween the revolving speed Nin and the torque Tin of the input shaft 14and the revolving speed Nout and the torque Tout of the output shaft 15are expressed by Equations (3) given below. The revolving speed Nout ofthe output shaft 15 at the second speed (2^(nd)) is higher than therevolving speed at the first speed (1^(st)), whereas the torque Tout ofthe output shaft 15 at the second speed (2^(nd)) is smaller than thetorque at the first speed (1^(st)).

Nout=Nin/k 2

Tout=k 2×Tin

k 2={ρ2(1+ρ3)+ρ3}/ρ2  (3)

where ρ2 and ρ3 respectively denote the gear ratios of the secondplanetary gear unit 130 and the third planetary gear unit 140.

In the case of the third speed (3^(rd)), the clutches C0 and C1, thebrake B2, and the one-way clutches F0 and F1 engage. Under theapplication of engine brake, the brake B1 further engages. This isequivalent to the state where the input shaft 14 of the transmission 100is directly linked with the sun gear 152 of the fourth planetary gearunit 150 and the ring gear 146 of the third planetary gear unit 140. Thesun gears 132 and 142 of the second and third planetary gear units 130and 140 are restricted not to rotate reversely by the functions of thebrake B2 and the one-way clutch F1. The revolving speeds of these sungears 132 and 142 are thus practically equal to zero. Like in the caseof the second speed (2^(nd)), under such conditions, according toEquations (1) given previously, the rotating conditions of the secondand third planetary gear units 130 and 140 are determined unequivocally,and the revolving speed of the output shaft 15 is determinedunequivocally. The relations between the revolving speed Nin and thetorque Tin of the input shaft 14 and the revolving speed Nout and thetorque Tout of the output shaft 15 are expressed by Equations (4) givenbelow. The revolving speed Nout of the output shaft 15 at the thirdspeed (3^(rd)) is higher than the revolving speed at the second speed(2^(nd)), whereas the torque Tout of the output shaft 15 at the thirdspeed (3^(rd)) is smaller than the torque at the second speed (2^(nd)).

Nout=Nin/k 3

Tout=k 3×Tin

k 3=1+ρ3  (4)

In the case of the fourth speed (4^(th)), the clutches C0 through C2 andthe one-way clutch F0 engage. The brake B2 simultaneously engages but isnot involved in transmission of the power. In this state, the clutchesC1 and C2 simultaneously engage, so that the input shaft 14 is directlylinked with the sun gear 132 of the second planetary gear unit 130, thesun gear 142 and the ring gear 146 of the third planetary gear unit 140,and the sun gear 152 of the fourth planetary gear unit 150. The thirdplanetary gear unit 140 thus integrally rotates with the input shaft 14at an identical revolving speed. The output shaft 15 thereby integrallyrotates with the input shaft 14 at an identical revolving speed. Theoutput shaft 15 rotates at a higher revolving speed in the fourth speed(4^(th)) than in the third speed (3^(rd)). The relations between therevolving speed Nin and the torque Tin of the input shaft 14 and therevolving speed Nout and the torque Tout of the output shaft 15 areexpressed by Equations (5) given below. The revolving speed Nout of theoutput shaft 15 at the fourth speed (4^(th)) is higher than therevolving speed at the third speed (3^(rd)), whereas the torque Tout ofthe output shaft at the fourth speed (4^(th)) is smaller than the torqueat the third speed (3^(rd)).

Nout=Nin/k 4

Tout=k 4×Tin

k 4=1  (5)

In the case of the fifth speed (5^(th)), the clutches C1 and C2 and thebrake B0 engage. The brake B2 simultaneously engages but is not involvedin transmission of the power. In this state, the clutch C0 disengages,so that the revolving speed is increased in the auxiliary transmissionunit 110. The revolving speed of the input shaft 14 of the transmission100 is increased and transmitted to the input shaft 119 of the primarytransmission unit 120. The clutches C1 and C2 engage simultaneously, sothat the input shaft 119 and the output shaft 15 rotate at an identicalrevolving speed, like in the case of the fourth speed (4^(th)).According to Equations (1) given previously, the relations between therevolving speeds and the torques of the input shaft 14 and the outputshaft 119 of the auxiliary transmission unit 110 are obtained, in orderto determine the revolving speed and: the torque of the output shaft 15.The relations between the revolving speed Nin and the torque Tin of theinput shaft 14 and the revolving speed Nout and the torque Tout of theoutput shaft 15 are expressed by Equations (6) given below. Therevolving speed Nout of t he output shaft 15 at the fifth speed (5^(th))is higher than the revolving speed at the fourth speed (4^(th)), whereasthe torque Tout of the output shaft 15 at the fifth speed (5^(th)) issmaller than the torque at the fourth speed (4^(th)).

Nout=Nin/k

Tout=k 5×Tin

k 5=1/(1+ρ1)  (6)

where ρ1 denotes the gear ratio of the first planetary gear unit 112.

In the case of reverse speed (R), the clutch C2 and the brakes B0 and B4engage. In this state, the revolving speed of the input shaft 14 isincreased in the auxiliary transmission unit 110 and linked with the sungear 132 of the second planetary gear unit 130 and the sun gear 142 ofthe third planetary gear unit 140. As described previously, the ringgear 136 and the planetary carriers 144 and 154 have an identicalrevolving speed. The ring gear 146 and the sun gear 152 also have anidentical revolving speed. The revolving speed of the ring gear 156 ofthe fourth planetary gear unit 150 becomes equal to zero by the functionof the brake B4. Under such conditions, according to Equations (1) givenpreviously, the rotating conditions of the respective planetary gearunits 130, 140, and 150 are determined unequivocally. At this moment,the output shaft 15 rotates in the negative direction to allow a reversemovement.

As described above, the transmission 100 of the embodiment can set theposition of the change-speed gear among the five forward speed and onereverse speed. The power input from the input shaft 14 is converted to adifferent combination of revolving speed and torque and output to theoutput shaft 15. The output power is defined by the increasing revolvingspeed and the decreasing torque in the sequence of the first speed(1^(st)) to the fifth speed (5^(th)). This is also true when a negativetorque, that is, a braking force, is applied to the input shaft 14. Thevariables k1 through k5 in Equations (2) through (6) given above denotethe gear ratios at the respective positions of the change-speed gear. Inthe case where a fixed braking force is applied to the input shaft 14 bymeans of the engine 10 and the motor 20, the braking force applied tothe output shaft 15 decreases in the 'sequence of the first speed(1^(st)) to the fifth speed (5^(th)). The transmission 100 may have avariety of known structures, other than the structure adopted in thisembodiment. The transmission 100 may have a greater number or a lessnumber of forward speeds.

The control unit 70 sets the position of the change-speed gear accordingto the vehicle speed and other conditions. The driver manually operatesa gearshift lever included in an operation unit 160 in the vehicle (seeFIG. 1), so as to select the gearshift position and vary the range ofthe change-speed gear. FIG. 4 shows the operation unit 160 for selectingthe gearshift position in the hybrid vehicle of this embodiment. Theoperation unit 160 is located along a longitudinal axis of the vehicleon the floor next to the driver's seat.

As shown in FIG. 4, the operation unit 160 includes a gearshift lever162. The driver slides the gearshift lever 162 along the longitudinalaxis of the vehicle, so as to select one among available gearshiftpositions. The available gearshift positions include a parking (P)position, a reverse (R) position, a neutral (N) position, a drive (D)position, a fourth position (4), a third position (3), a second position(2), and a low position (L), which are arranged in this order from theforward of the vehicle.

The parking (P), the reverse (R), and the neutral (N) positionscorrespond to the engagement states shown in FIG. 3. At the driveposition (D), the selected mode enables a drive using the first speed(1^(st)) to the fifth speed (5^(th)). At the fourth position (4), theselected mode enables a drive using the first speed (1^(st)) to thefourth speed (4^(th)). In a similar manner, the selected mode at thethird position (3), the second position (2), and the low position (L)respectively enables a drive using the first speed (1^(st)) to the thirdspeed (3^(rd)), using the first speed (1^(st)) to the second speed(2^(nd)), and using only the first speed (1^(st)).

In the hybrid vehicle of the embodiment, the driver can arbitrarily setthe deceleration by the power-source braking as discussed later. Theoperation unit 160 for selecting the gearshift position has a mechanismfor setting the deceleration.

As shown in FIG. 4, in the hybrid vehicle of the embodiment, thegearshift lever 162 may be slid sideways at the drive (D) position, aswell as slid in the longitudinal direction for selecting the gearshiftposition. The position selected in this way is called an E position.When the gearshift lever 162 is at the E position, the setting of thedeceleration by the power-source braking may be varied by operating thegearshift lever 162 in the longitudinal direction as discussed below.The operation unit 160 includes a sensor for detecting the selectedgearshift position and an E position switch that is turned on when thegearshift lever 162 is at the E position. The signals of these sensorand switch are transmitted to the control unit 70 and used for thevarious control operations in the vehicle as discussed later.

The following describes the operation when the gearshift lever 162 is atthe E position. The gearshift lever 162 is kept in the middle of the Eposition, that is, the neutral state, while the driver does not hold thegearshift lever 162. When the driver desires to increase thedeceleration, that is, abrupt braking is required, the driver pressesback the gearshift lever 162 (to the side of Decel). When the driverdesires to decrease the deceleration, that is, gentle braking isrequired, the driver presses forward the gearshift lever 162 (to theside of Can-Decel). The gearshift lever 162 is not continuously slid inthe longitudinal direction at the E position but is moved stepwise.Namely the gearshift lever 162 may be set in one of the three states,that is, the neutral state, the Can-Decel state (pressed forward), andthe Decel state (pressed back), at the E position. When the driverreleases the force applied to the gearshift lever 162, the gearshiftlever 162 immediately returns to the neutral state. The deceleration bythe power-source braking is varied in a stepwise manner according to thefrequency of operation of the gearshift lever 162 in the longitudinaldirection.

The hybrid vehicle of the embodiment has operation elements mounted on asteering wheel to vary the deceleration by the power-source braking, inaddition to the operation of the gearshift lever 162. FIG. 5 shows theoperation elements mounted on a steering wheel 164. FIG. 5(a) shows thesurface of the steering wheel 164, that is, the side facing the driver.A pair of Decel switches 166L and 166R are placed on a spoke of thesteering wheel 164 to increase the deceleration. The positions of theseswitches 166L and 166R are specified to allow an easy manual operationwith the left thumb or the right thumb while the driver handles thesteering wheel. In this embodiment, the two switches 166L and 166R havean identical function, in order to ensure the adequate operation withoutany confusion even in the event that the steering wheel 164 is rotated.

FIG. 5(b) shows the rear face of the steering wheel 164. A pair ofCan-Decel switches 168L and 168R are mounted at practically reversepositions of the Decel switches 166L and 166R to decrease thedeceleration. The positions of these switches 168L and 168R are alsospecified to allow an easy manual operation with the left index fingeror the right index finger while the driver handles the steering wheel.Because of the same reason as discussed above for the Decel switches166L and 166R, the two switches 168L and 168R have an identicalfunction.

When the driver presses the Decel switch 166L or 166R, the decelerationis increased according to the frequency of pressing the switch. When thedriver presses the Can-Decel switch 168L or 168R, on the other hand, thedeceleration is decreased according to the frequency of pressing theswitch. These switches 166L, 166R, 168L, and 168R are effective only inthe case where the gearshift lever 162 is at the E position (see FIG.4). This arrangement effectively prevents the setting of the targetdeceleration from being changed unintentionally by accidental presses ofthese switches 166L, 166R, 168L, and 168R while the driver handles thesteering wheel 164.

The operation unit 160 also has a snow mode switch 163. The driverpresses the snow mode switch 163 when the road surface has a lowfriction coefficient and is in a slippery condition, for example, in thecase of snow-covered road. In the ON position of the snow mode switch163, the upper limit of the target deceleration is restricted to be notgreater than a preset level as discussed later. The speed reduction by alarge deceleration during a drive on the road surface having a lowfriction coefficient may cause a slip or a skid of the vehicle. In theON position of the snow mode switch 163, the deceleration is restrictedto be not greater than the preset level, so as to prevent a slip or askid of the vehicle. In the ON position of the snow mode switch 163, thedeceleration may be changed in a certain range that does not cause aslip or a skid of the vehicle.

The operation unit for selecting the gearshift position and setting thetarget deceleration is not restricted to the structure of the embodiment(shown in FIG. 4), but may have any suitable structure. FIG. 6 showsanother operation unit 160A having a modified structure. The operationunit 160A is arranged along the longitudinal axis of the vehicle on thefloor next to the driver's seat. The driver slides the gearshift lever162 in the longitudinal direction to select one among various gearshiftpositions. Although the fourth to the low positions are omitted from theillustration of FIG. 6, the operation unit 160A of the modifiedstructure may also have these gearshift positions like the operationunit 160 shown in FIG. 4. The operation unit 160A of the modifiedstructure has the E position at the rear of the normal movable range forselecting the gearshift position. The driver slides the gearshift lever162 along the longitudinal axis of the vehicle at the E position, so asto vary the setting of the deceleration continuously. In this example,the deceleration increases with a backward slide of the gearshift lever162, and decreases with a forward slide of the gearshift lever 162. Thismodified structure is only an example, and there are a variety of otherstructures applicable for the mechanism of setting the deceleration.

The setting of the deceleration is displayed on an instrument panel inthe vehicle. FIG. 7 shows an instrument panel in the hybrid vehicle ofthis embodiment. The instrument panel is placed in front of the driverlike the standard vehicle. A fuel gauge 202 and a speedometer 204 aredisposed on the left side of the instrument panel seen from the driver.An engine temperature gauge 208 and a tachometer 206 are disposed on theright side of the instrument panel. A gearshift position indicator 220is arranged on the center of the instrument panel to display thegearshift position. Direction indicators 210L and 210R are set on bothsides of the gearshift position indicator 220. These instruments arealso found in the standard vehicle. In the hybrid vehicle of thisembodiment, in addition to these instruments, an E position indicator222 is provided above the gearshift position indicator 220. Adeceleration indicator 224 is also set on the right side of the Eposition indicator 222 to display the deceleration currently set.

The E position indicator 222 lights up when the gearshift lever 162 isset at the E position. When the driver presses the Decel switches or theCan-Decel switches to set the deceleration, the length of a rearwardarrow (rightward arrow in FIG. 7) displayed with a symbol of the vehiclein the deceleration indicator 224 is varied to sensuously express thesetting of the deceleration. In the hybrid vehicle of the embodiment,the setting of the deceleration may be restricted according to a varietyof conditions as discussed later. In the case where the setting of thedeceleration is restricted, the E position indicator 222 and thedeceleration indicator 224 flicker or give a display of different form,so as to inform the driver of the restricted setting of thedeceleration.

In the hybrid vehicle of the embodiment, the control unit 70 controlsthe operations of the engine 10, the motor 20, the torque converter 30,and the transmission 100 (see FIG. 1). The control unit 70 isconstructed as a one-chip microprocessor including a CPU, a RAM, and aROM. The CPU carries out various control operations discussed belowaccording to programs recorded in the ROM. A variety of input and outputsignals are connected to the control unit 70 to implement the controloperations. FIG. 8 shows connections of input and output signals intoand from the control unit 70. The left side of FIG. 8 shows the signalsinput into the control unit 70, whereas the right side shows the signalsoutput from the control unit 70.

The signals input into the control unit 70 are received from variousswitches and sensors. The input signals represent, for example, theon-off state of a hybrid cancel switch to set a drive only with theengine 10 as the power source, the acceleration of the vehicle measuredwith an acceleration sensor, the speed of the engine 10, the watertemperature of the engine 10, the on-off state of an ignition switch,the remaining charge SOC of the battery 50, the crank position of theengine 10, the on-off state of a defogger, the driving condition of anair conditioner, the vehicle speed, the oil temperature of the torqueconverter 30, the gearshift position (see FIG. 4), the on-off state of aparking brake, the amount of actuation of the brake pedal, thetemperature of a catalyst for converting the exhaust of the engine 10,the travel of the accelerator, the on-off state of an auto cruiseswitch, the on-off state of the E position switch (see FIG. 4), thestates of the Decel switch and the Can-Decel switch to change thesetting of the target deceleration, the turbine speed of a supercharger,the on-off state of the snow mode switch to set a drive mode on the roadsurface having a low friction coefficient, such as the snow-coveredroad, and the level of the fuel measured by the fuel gauge. In thisembodiment, the vehicle speed is calculated from the numbers ofrotations of the left and right driving wheels 18L and 18R.

The signals output from the control unit 70 are used to control theengine 10, the motor 20, the torque converter 30, and the transmission100. The output signals include, for example, an ignition signal toregulate the ignition timing of the engine 10, a fuel injection signalto control the fuel injection, a starter signal to start the engine 10,an MG control signal to carry out the switching in the driving circuit40 and control the operation of the motor 20, a transmission controlsignal to change over the position of the change-speed gear in thetransmission 100, an AT solenoid signal and an AT line pressure controlsolenoid signal to regulate the hydraulic pressure in the transmission100, a signal for regulating an actuator of an anti-lock braking system(ABS), a driving source indicator signal to display the source of thedriving force, a control signal of the air conditioner, control signalsfor various alarms, a control signal of an electronic throttle valve ofthe engine 10, a snow mode indicator signal to display the selection ofthe snow mode, a VVT signal to regulate the open and close timings ofthe intake valve and the exhaust valve of the engine 10, a systemindicator signal to display the driving state of the vehicle, and adeceleration indicator signal to display the deceleration set currently.

A2. General Operations

The following describes the general operation of the hybrid vehicle ofthis embodiment. As discussed previously with FIG. 1, the hybrid vehicleof this embodiment has the engine 10 and the motor 20 as the powersource. The control unit 70 selectively uses the engine 10 and themotor: 20 according to the driving state of the vehicle, that is,according to the vehicle speed and the torque. The adequate selection isset in advance in the form of a map and stored in the ROM included inthe control unit 70.

FIG. 9 is a map showing the relationship between the driving state ofthe vehicle and the power source. A Curve LIM represents the limit of anoperable area of the vehicle. An area MG denotes a driving area in whichthe motor 20 is used as the power source, and an area EG denotes adriving area in which the engine 10 is used as the power source.Hereinafter the former is referred to as the EV drive and the latter asthe standard drive. The structure of FIG. 1 allows the hybrid vehicle tobe driven with both the engine 10 and the motor 20 as the power source,but this embodiment does not set such a driving area.

As shown in this map, the hybrid vehicle of this embodiment starts atthe EV drive. As described previously (see FIG. 1), in the hybridvehicle of the embodiment, the engine 10 and the motor 20 integrallyrotate with each other. Even in the course of the EV drive, the engine10 accordingly rotates, but is motored without fuel injection andignition. As described previously, the engine 10 has the VVT mechanism.The control unit 70 controls the VVT mechanism and delays the open andclose timings of the intake valve and the exhaust valve, in order toreduce the load applied to the motor 20 during the EV drive and enablethe power output from the motor 20 to be effectively used for drivingthe vehicle.

When the vehicle starting at the EV drive reaches a driving state closeto the boundary between the area MG and the area EG in the map of FIG.9, the control unit 70 starts the engine 10. Since the engine 10 hasalready been rotated at a predetermined speed by means of the motor 20,the control unit 70 simply carries out the fuel injection to the engine10 and the ignition at a preset timing. The control unit 70 alsocontrols the VVT mechanism to change the open and close timings of theintake valve and the exhaust valve to the timings suitable for theoperation of the engine 10.

After the engine 10: starts, the vehicle is driven with only the engine10 as the power source in the area EG. In response to the start of thedrive in the area EG, the control unit 70 shuts down all the transistorsincluded in the driving circuit 40. This causes the motor 20 to idle.

The control unit 70 carries out the control procedures to change thepower source according to the driving state of the vehicle as well as tochange over the position of the change-speed gear in the transmission100. Like the changeover of the power source, the changeover of theposition of the change-speed gear is implemented, based on a map thathas been set in advance according to the driving state of the vehicle.FIG. 10 is a map showing the relationship between the position of thechange-speed gear in the transmission 100 and the driving state of thevehicle. The control unit 70 changes over the position of thechange-speed gear, in order to attain a smaller gear ratio with anincrease in vehicle speed as shown in this map.

The changeover of the position of the change-speed gear is under therestriction of the gearshift position. At the drive (D) position, thevehicle is driven using the change-speed gear up to the fifth speed(5^(th)). At the fourth position (4), the vehicle is driven using thechange-speed gear up to the fourth speed (4^(th)). In the latter case,the fourth speed (4^(th)) is used even in the area of the 5^(th) in themap of FIG. 10. The position of the change-speed gear is changedaccording to the map, as well as by a kick down control. The kick downcontrol changes over the position of the change-speed gear to a positionof a larger gear ratio by one step, when the driver slams down on theaccelerator pedal. These control procedures are identical with thosecarried out in the known vehicle with an automatic transmission. Thehybrid vehicle of this embodiment carries out the similar controlprocedures during the EV drive (that is, in the area MG). Therelationship between the position of the change-speed gear and thedriving state of the vehicle is not restricted to the map of FIG. 10,but may be set adequately according to the gear ratio of thetransmission 100.

The maps of FIGS. 9 and 10 are used in the case where both the EV driveand the standard drive are selectively performed according to thedriving state of the vehicle. The control unit 70 of the embodiment alsohas maps used in the case where only the standard drive is performedover the whole driving state of the vehicle. These maps omit the area ofthe EV drive (that is, the area MG) from the maps of FIGS. 9 and 10. TheEV drive requires the battery 50 to store a certain level of electricpower. The control unit 70 accordingly selects the right map accordingto the charging state of the battery 50 and carries out the control ofthe vehicle. When the remaining charge SOC of the battery 50 is not lessthan a preset level, the control unit 70 carries out the control toselectively perform both the EV drive and the standard drive based onthe maps of FIGS. 9 and 10. When the remaining charge SOC of the battery50 is less than the preset level, on the other hand, the control unit 70carries out the control to perform the standard drive only with theengine 10 as the power source even at the time of starting and duringthe low-speed run. The selection of the right map is repeatedly carriedout at predetermined time intervals. In some cases, the remaining chargeSOC of the battery 50 is not less than the preset level and the vehiclestarts at the EV drive, but the consumption of electric power after thestart makes the remaining charge SOC less than the preset level. In thiscase, the control unit 70 changes the EV drive to the standard driveeven when the driving state of the vehicle is within the area MG.

The following describes the braking in the hybrid vehicle of theembodiment. The hybrid vehicle of the embodiment adopts both the wheelbraking applied in response to actuation of the brake pedal and thepower-source braking by means of the loading torques from the engine 10and the motor 20. The power-source braking is made effective when theaccelerator pedal is released. The target deceleration by thepower-source braking is reduced with a decrease in vehicle speed. Namelythe magnitude of the power source braking is reduced with a decrease invehicle speed. In the event that the driver steps on the brake pedal,the braking force applied to the vehicle is the sum of the power-sourcebraking and the wheel braking.

In the hybrid vehicle of the embodiment, the driver performs thespecific operation at the E position, so as to set the deceleration bythe power-source braking. The operation of the Decel switch at the Eposition increases the deceleration by the power-source braking in astepwise manner. The operation of the Can-Decel switch at the Eposition, on the other hand, decreases the deceleration by thepower-source braking in a stepwise manner.

The hybrid vehicle of the embodiment implements the power-source brakingset in the stepwise manner as a combination of the changeover of theposition of the change-speed gear in the transmission 100 with thebraking force by the motor 20. FIG. 11 is a map showing the combinationsof the vehicle speed, the deceleration, and the position of thechange-speed gear in the hybrid vehicle of the embodiment. In the map ofFIG. 11, the deceleration is expressed as absolute values. The operationof either the Decel switch or the Can-Decel switch causes thedeceleration of the vehicle to be varied in a stepwise manner in a rangebetween straight lines BL and BU shown in FIG. 11.

The deceleration by the power-source braking is varied in a certainrange by regulating the torque of the motor 20. The changeover of theposition of the change-speed gear in the transmission 100 varies theratio of the torque of the power source to the torque output to the axle17. This enables the deceleration of the vehicle to be changed accordingto the position of the change-speed gear. When the position of thechange-speed gear is at the second speed (2^(nd)), regulating the torqueof the motor 20 attains the deceleration in a range defined by theshort-dashed lines in FIG. 11. At the third speed (3^(rd)), theregulation of the torque attains the deceleration in a range defined bythe solid lines in FIG. 11. At the fourth speed (4^(th)), the regulationof the torque attains the deceleration in a range defined by the one-dotchain lines in FIG. 11. At the fifth speed (5^(th)), the regulation ofthe torque attains the deceleration in a range defined by thelong-dashed lines in FIG. 11.

The control unit 70 selects the position of the change-speed gear toattain the preset deceleration based on the map of FIG. 11 and carriesout the braking control. For example, when the deceleration is set onthe straight line BL in FIG. 11, in an area of higher vehicle speed thana value Vc, the braking control is performed at the fifth speed(5^(th)). In the area of lower vehicle speed than the value Vc, on theother hand, the braking control is performed after the position of thechange-speed gear is changed to the fourth speed (4^(th)). In this area,the desired deceleration is not attained at the fifth speed (5^(th)). Inthe arrangement of this embodiment, the range of the decelerationattained at each position of the change-speed gear overlaps the rangesof deceleration attained at the adjacent positions of the change-speedgear. In the area of higher vehicle speed than the value Vc, thedeceleration corresponding to the straight line BL may be attained atboth the fourth speed (4^(th)) and the fifth speed (5^(th)). In thisarea, the control unit 70 selects the position of the change-speed gearmore suitable for the braking, either the fourth speed (4^(th)) or thefifth speed (5^(th)), based on a variety of conditions, and carries outthe braking control.

The settings at the respective positions of the change-speed gear in theembodiment are described more in detail. FIG. 12 is a map showing therelationship between the deceleration and the position of thechange-speed gear at a certain vehicle speed Vs. The map of FIG. 12corresponds to the relationship between the deceleration and theposition of the change-speed gear along a straight line Vs in the map ofFIG. 11. As shown in the map of FIG. 12, in a division D1 of arelatively low deceleration, the target deceleration is attained only atthe fifth speed (5^(th)). In a division D2 of a higher deceleration, thetarget deceleration is attained at both the fifth speed (5^(th)) and thefourth speed (4^(th)). In a similar manner, the respective targetdecelerations are attained only at the fourth speed (4^(th)) in adivision D3, at both the third speed (3^(rd)) and the fourth speed(4^(th)) in a division D4, only at the third speed (3^(rd)) in adivision D5, at both the second speed (2^(nd)) and the third speed(3^(rd)) in a division D6, and only at the second speed (2^(nd)) in adivision D7, where the deceleration increases in the order of thedivision D3 to the division D7. Although the map described here is forthe braking control up to the second speed (2^(nd)), the map may alsoinclude the setting at the first speed (1^(st)).

The following gives the reason why the range of deceleration attained ateach position of the change-speed gear overlaps the adjacent ranges ofdeceleration. FIG. 13 is a graph showing a variation in deceleration atthe second speed (2^(nd)). Dashed lines TL and TU respectively representthe lower limit and the upper limit of deceleration attained at thesecond speed (2^(nd)). A solid line TE represents the decelerationattained only by engine brake of the engine 10. In the hybrid vehicle ofthe embodiment, the control of the VVT mechanism enables thedeceleration by engine brake to be varied. Such control, however, haspoor response and low accuracy. The technique of the embodimentaccordingly does not control the VVT mechanism in the course of braking.The deceleration by engine brake is thus unequivocally determinedcorresponding to the vehicle speed as shown in FIG. 13.

In the hybrid vehicle of this embodiment, the deceleration is varied byregulating the torque of the motor 20. In a hatched area Bg of FIG. 13,the motor 20 carries out the regenerative operation and applies anadditional braking force, thereby attaining a higher deceleration thanthe deceleration only by engine brake. In another area Bp, which isdefined by the straight line TE and the dashed line TL, the motor 20carries out the power operation and outputs a driving force, therebyattaining a lower deceleration than the deceleration only by enginebrake.

FIG. 14 schematically illustrates the comparison between a brakingtorque in the case where the motor 20 carries out the regenerativeoperation and a braking torque in the case where the motor 20 carriesout the power operation. The left bar in the graph shows the brakingtorque when the motor 20 carries out the power operation (that is, thestate in the area Bp). The braking torque by engine brake is expressedas a bar BE. In the area Bp, the motor 20 outputs a driving forceexpressed as a bar BM in reverse of the direction of the braking torqueBE by engine brake. The total braking torque, which is obtained as thesum of the braking torque by engine brake and the driving force by themotor 20, is output to the axle 17. The output braking torque isaccordingly smaller than the braking torque BE by engine brake as shownin a hatched area.

The right bar in the graph shows the braking torque when the motor 20carries out the regenerative operation (that is, the state in the areaBg). It is assumed that the braking torque BE by engine brake in thearea Bg is identical with the braking torque BE in the area Bp. In thearea Bp, the motor 20 outputs an additional braking torque expressed asa bar BM in the same direction as that of the braking torque by enginebrake. The total braking torque, which is obtained as the sum of thebraking torque by engine brake and the additional braking torque by themotor 20, is output to the axle 17. The output braking torque isaccordingly greater than the braking torque BE by engine brake as shownin a hatched area.

The hybrid vehicle of the embodiment changes the driving state of themotor 20 between the regenerative operation and the power operation, soas to attain the higher deceleration and the lower deceleration than thedeceleration only by engine brake. The map of FIG. 11 is set to make thearea of deceleration attained by the power operation of the motor 20 ata specific position of the change-speed gear having a greater gear ratiooverlap the area of deceleration attained by the regenerative operationof the motor 20 at a specific position of the change-speed gear having asmaller gear ratio. For example, the braking area by the power operationof the motor 20 at the second speed (2^(nd)) is made to overlap thebraking area by the regenerative operation of the motor 20 at the thirdspeed (3^(rd)).

This arrangement ensures the braking control according to the remainingcharge SOC of the battery 50. In the case where the battery 50 is in astate that allows further charging, the position of the change-speedgear having a smaller gear ratio is selected to attain the desireddeceleration by the regenerative operation of the motor 20. In the casewhere the battery 50 is in a state that is close to the full charge, onthe other hand, the position of the change-speed gear having a greatergear ratio is selected to attain the desired deceleration by the poweroperation of the motor 20. The technique of the embodiment sets theareas of deceleration at two adjacent positions of the change-speed gearin an overlapping manner, thereby attaining the desired decelerationirrespective of the remaining charge SOC of the battery 50.

The above settings are only one example, where the area of decelerationat each position of the change-speed gear overlaps the areas ofdeceleration at the adjacent positions of the change-speed gear as shownin the map of FIG. 11. One possible modification sets the area ofdeceleration attained at each position of the change-speed gear in anon-overlapping manner. Another possible modification sets the area ofdeceleration attained at each position of the change-speed gear partlyin an overlapping manner.

The deceleration set in the above manner corresponds to the lower limitof the power-source braking applied to the vehicle. Here it is assumedthat the deceleration is set on the straight line BL. In the case wherethe position of the change-speed gear is at the third speed (3^(rd)) inthe area of higher vehicle speed than Vc, the actual deceleration isalways greater than the deceleration corresponding to the straight lineBL. Since the lower limit of deceleration is set in the hybrid vehicleof the embodiment, the desired deceleration is attained. In this case,the control procedure does not change over the position of the changespeed gear to the fourth speed (4^(th)) or the fifth speed (5^(th)) toattain a relatively low deceleration corresponding to the straight lineBL. In the event that the driver presses the Can-Decel switch to lowerthe setting of the deceleration, the position of the change-speed gearshould be changed to attain the deceleration required by the driver.

As described above, the technique of this embodiment enables the brakingcontrol with the deceleration set by the driver. Such braking control iscarried out when the gearshift lever is in the E position, and ishereinafter referred to as the E position braking control. The standardbraking control is performed in the case where the gearshift lever isout of the E position. The standard braking control does not change overthe position of the change-speed gear, unlike the E position brakingcontrol. The standard braking control accordingly implements the brakingat the position of the change-speed gear set at the time when thepower-source braking starts application. When the gearshift lever is setin the drive position (D), the vehicle is generally driven at the fifthspeed (5^(th)). The braking is thus performed at a relatively lowdeceleration that can be attained at the fifth speed (5^(th)). When thegearshift lever is set in the fourth position (4), the vehicle is drivenup to the fourth speed (4^(th)), the braking is performed at a littlehigher deceleration than that in the drive position (D). In the case ofstandard braking control, the motor 20 carries out the regenerativeoperation where a braking force gives a certain load. The standardbraking control does not allow the wide range of deceleration at eachposition of the change-speed gear as shown in the map of FIG. 11, butattains only the deceleration along one straight line at each positionof the change-speed gear.

A3. Drive Control Process

In the hybrid vehicle of the embodiment, the control unit 70 controlsthe operations of the engine 10 and the motor 20, so as to enable thedriving discussed above. The following describes the details of thespeed reduction control in the course of braking operation, which ischaracteristic of the hybrid vehicle of the embodiment.

FIG. 15 is a flowchart showing a speed reduction control routine, whichis executed at predetermined time intervals by the CPU included in thecontrol unit 70. When the program enters the speed reduction controlroutine of FIG. 15, the CPU first carries out an initial setting process(step S10). The initial setting process includes the procedure ofsetting the initial value of the target deceleration required for thespeed reduction control and canceling the setting of the targetdeceleration. The initial setting process is carried out every time theexecution of the speed reduction control routine is repeated.

FIG. 16 is a flowchart showing a routine of the initial setting process.In the initial setting process routine, the CPU first receives signalsfrom various switches (step S15). The signals input here are those shownin FIG. 8. The signals directly relating to the initial setting processroutine are only the gearshift position signal and the E position switchsignal. The processing of step S15 may accordingly input only thegearshift position signal and the E position switch signal.

The CPU then determines whether or not the gearshift position has beenchanged from the D position to the E position, based on the inputsignals (step S20). In the case where the currently input gearshiftposition is the E position and the previously input gearshift positionis the D position, the CPU determines that the above change has beenimplemented. The determination may alternatively be carried out, basedon the change of the state of the E position switch from the OFFposition to the ON position.

When it is determined that the gearshift position has been changed fromthe D position to the E position, the E position indicator (see FIG. 7)is turned on (step S40). An ON signal for turning the E positionindicator on is output as the system indicator signal shown in FIG. 8.The E position indicator lights up in response to this ON signal.Simultaneously with the light-up of the E position indicator, the CPUsets an initial value corresponding to the D position to the targetdeceleration (step S45).

In the case where the power-source braking starts application at thefifth speed (5^(th)) while the gearshift lever is set in the D position,the processing of step S45 sets the target deceleration corresponding tothe deceleration attained at the fifth speed (5^(th)) as the initialvalue. In this embodiment, as shown in the map of FIG. 11, in the areaof low vehicle speed, the minimum possible deceleration (defined by thestraight line BL) may be higher than the deceleration attained at thefifth speed (5^(th)). Although not specifically shown in the flowchart,the setting of the target deceleration at step S45 is performed only inthe possible range of deceleration at the E position. When thedeceleration attained at the D position is lower than the minimumpossible deceleration (the straight line BL) at the E position, thevalue corresponding to the straight line BL is set to the targetdeceleration. The initial setting of the target deceleration accordinglydepends upon the position of the change-speed gear used in the Dposition. Namely the initial setting of the target deceleration isequivalent to the deceleration attained at the D position in the area ofrelatively high vehicle speed. The initial setting of the targetdeceleration may, however, be higher than the deceleration attained atthe D position in the area of relatively low vehicle speed.

One modified processing of step S45 unconditionally sets an initialvalue higher than the deceleration attained at the D position to thetarget deceleration. In many cases, the driver desires to change thedeceleration at the E position when feeling insufficiency of thedeceleration attained at the D position. Setting the initial valuehigher than the deceleration at the D position to the targetdeceleration at step S45 enables the deceleration required by the driverto be attained quickly. The processing of step S45 sets the initialvalue of the target deceleration at the E position, based on thedeceleration attained at the D position. This arrangement enables thedriver to easily estimate the value of deceleration immediately afterthe change of the gearshift position to the E position. This facilitatesthe setting of the deceleration at the E position and reduces the senseof incompatibility at the time of change to the E position.

The CPU then sets the position of the change-speed gear used in the Dposition to an initial position of the change-speed gear (step S50). Asdescribed previously, the hybrid vehicle of the embodiment regulates thetorque of the motor 20 in combination with the changeover of theposition of the change-speed gear at the E position, thereby attainingthe braking at the target deceleration. The target deceleration hererepresents the minimum deceleration desired by the driver. In the casewhere the deceleration corresponding to the straight line BL in the mapof FIG. 11 is set to the target deceleration, the position of thechange-speed gear attaining the desired deceleration at the vehiclespeed Vs can be selected among the second speed (2^(nd)) through thefifth speed (5^(th)). The processing of step S50 sets the position ofthe change-speed gear used in the D position among the possiblealternatives to the initial value. This arrangement prevents theposition of the change-speed gear from being changed simultaneously withthe change of the gearshift position to the E position. This favorablyreduces possible shocks at the time of the change to the E position.

When it is determined at step S20 that the gearshift position has notbeen changed from the D position to the E position, on the other hand,the CPU determines whether or not the gearshift position has bee changedfrom the E position to the D position (step S25). In the case where thecurrently input gearshift position is the D position and the previouslyinput gearshift position is the E position, the CPU determines that theabove change has been implemented. The determination may alternativelybe carried out, based on the change of the state of the E positionswitch from the ON position to the OFF position.

When it is determined that the gearshift position has been changed fromthe E position to the D position, the E position indicator (see FIG. 7)is turned off (step S30). An OFF signal for turning the E positionindicator off is output as the system indicator signal shown in FIG. 8.The E position indicator lights out in response to this OFF signal.Simultaneously with the light-out of the E position indicator, the CPUcancels the current setting of the target deceleration (step S35). Thedriver operates the Decel switch and the Can-Decel switch to set thedesired deceleration during the drive at the E position as discussedlater. The processing of step S35 cancels such setting of the desireddeceleration.

In many cases, the deceleration required by the driver varies accordingto the driving state of the vehicle. There is accordingly not muchnecessity of storing the setting of the target deceleration as theprovision for the next selection of the E position. The driver rarelyremembers the previous setting of the target deceleration. The structureof not canceling the current setting of the target deceleration butusing the current setting in the case of next selection of the Eposition may cause the braking control to be performed with thedeceleration against the expectation of the driver, simultaneously withthe change of the gearshift position to the E position. In order toprevent such troubles, the technique of this embodiment cancels thecurrent setting of the target deceleration every time the gearshiftposition is changed from the E position to the D position.

A variety of techniques other than that discussed above may be appliedto cancel the setting of the target deceleration. One availabletechnique cancels the setting of the target deceleration every time thegearshift position is changed from the D position to the E position,instead of from the E position to the D position. The procedure of thisembodiment sets the initial value of the target deceleration regardlessof the previous setting at the time of the change to the E position. Theprocessing of step S35 to cancel the setting may thus be omitted. Anoperation of canceling the setting the target deceleration may beprovided separately. In this case, the setting of the targetdeceleration is not cancelled at the time of the change of the gearshiftposition from the E position to the D position, but is cancelled only inresponse to a specific operation, for example, an operation of a cancelswitch.

As described above, the CPU carries out the initial setting of thetarget deceleration and the position of the change-speed gear or thecancellation of the setting of the target deceleration at the time ofthe change of the gearshift position to the E position or to the Dposition, and exits from the initial setting process routine. When it isdetermined at step S25 that the gearshift position has not been changedfrom the E position to the D position, that is, when the gearshiftposition has been kept at the E position or at the D position, theinitial setting process does not require the change of the settings ofthe target deceleration and the position of the change-speed gear. TheCPU accordingly exits from the initial setting process routine withoutany further processing.

Referring back to the flowchart of FIG. 15, after the conclusion of theinitial setting process routine, the CPU carries out a decelerationsetting process (step S100). The deceleration setting process sets thedeceleration to be attained at the E position, in response to theoperations of the Decel switch and the Can-Decel switch. The details ofthe deceleration setting process are described with reference to FIG.17.

FIG. 17 is a flowchart showing a routine of the deceleration settingprocess. When the program enters the deceleration setting processroutine, the CPU first receives signals from various switches (stepS105). The signals input here are the Decel switch signal, the Can-Decelswitch signal, the E position switch signal, and the snow mode switchsignal among the various signals shown in FIG. 8, although the othersignals may be additionally input.

The CPU determines whether or not the E position has been selected,based on the input signals (step S110). More specifically thedetermination is based on the on-off state of the E position switch.When the E position has not been selected, the CPU determines that thereis no necessity of changing the setting of the deceleration and exitsfrom the deceleration setting process routine without any furtherprocessing.

When it is determined at step S110 that the E position has beenselected, on the other hand, the CPU subsequently determines whether ornot there is any failure with regard to the Decel switch and theCan-Decel switch (step S115). A variety of techniques are applicable todetect the possible failure. For example, in the case of a contactfailure of the switch, chattering occurs to cause extremely frequentswitch-over between the ON position and the OFF position. The detectionof the on-off change at a frequency of or over a predetermined level fora preset time period leads to detection of the switch failure. On thecontrary, the detection of the continuous switch-on state for a longertime period than expected from the standard operation also leads todetection of the switch failure.

When any failure of the switch is detected, the CPU cancels the currentsetting of the target deceleration (step S170), in order to prevent thedeceleration from being set against the intention of the driver. Theprocessing may alternatively keep the current setting of the targetdeceleration unchanged. The processing adopted in this embodiment takesinto account the possibility that there is a failure of the switch whilethe driver corrects the deceleration set against the intention of thedriver, and cancels the current setting of the target deceleration.After the cancellation of the setting of the target deceleration, theCPU gives a failure display, so as to inform the driver of the switchfailure (step S175). A variety of techniques may be applied for thefailure display. The technique adopted in this embodiment gives a soundalarm while flashing the E position indicator (see FIG. 7). These alarmsare given by outputting adequate signals as the alarm signal and thesystem indicator signal shown in FIG. 8.

The CPU then prohibits the E position braking control (step S180). Aconcrete process of step S180 in this embodiment sets a prohibitionflag, which is used to prohibit braking at the E position. As discussedlater, in the actual process of braking control, braking at the Eposition is prohibited or allowed by the set and reset of theprohibition flag. This arrangement causes the braking controlcorresponding to the D position to be performed, whether or not thegearshift lever is at the E position. In the case of the switch failure,the CPU carries out the above processing and then exits from thedeceleration setting process routine.

When it is determined at step S115 that there is no switch failure, theCPU shifts to the processing to change the setting of the targetdeceleration. The CPU first determines whether or not the Decel switchand the Can-Decel switch are operated simultaneously (step S120). In thecase of the simultaneous operation of both the switches, it is unclearwhich of these switches is preferential. The CPU accordingly skips thesubsequent process of changing the setting of the target decelerationand keeps the current setting of the target deceleration unchanged.

As shown in FIGS. 4 and 5, the hybrid vehicle of the embodiment sets thetarget deceleration with the switches provided on the gearshift leverand the steering wheel. There is a possibility that the driversimultaneously operates the switch on the gearshift lever and the switchon the steering wheel by accident or by mistake. The technique of theembodiment maintains the current setting of the target deceleration inthe case of the simultaneous operation of both the Decel switch and theCan-Decel switch, in order to prevent the setting of the targetdeceleration from being changed by the wrong operation against theintention of the driver.

In the case of non-simultaneous operation of the Decel switch and theCan-Decel switch, on the other hand, the setting of the targetdeceleration is changed in response to the corresponding switchoperation. When it is determined that the Decel switch is on (stepS125), the CPU increases the value of the target deceleration (stepS130). When it is determined that the Can-Decel switch is on (stepS135), on the contrary, the CPU decreases the value of the targetdeceleration (step S140). In the procedure of this embodiment, thesetting of the target deceleration is changed stepwise according to thefrequency of operation of the corresponding switch. In the case of nooperation of either switch, the setting of the target deceleration isnaturally not changed.

After setting the target deceleration by the processing discussed above(steps S120 through S140), the CPU carries out a decelerationrestricting process (step S145). FIG. 18 is a flowchart showing aroutine of the deceleration restricting process. In the decelerationrestricting process routine, the CPU first receives the signal of thesnow mode switch (see FIG. 4) (step S146). The technique of thisembodiment changes the upper limit of deceleration, based on the on-offstate of the snow mode switch. When it is determined that the snow modeswitch is off, that is, in the case of non-snow mode (step S148), theCPU determines that there is no necessity of restricting thedeceleration and immediately exits from the deceleration restrictingprocess routine.

When it is determined that the snow mode switch is on, that is, in thecase of snow mode (step S148), on the other hand, the targetdeceleration currently set by the processing of steps S125 through S140in the deceleration setting process routine is compared with an upperlimit DLIM (step S150). In the case where the target deceleration is nothigher than the upper limit DLIM, the CPU determines that there is nonecessity of restricting the deceleration and exits from thedeceleration restricting process routine without any further processing.In the case where the target deceleration is higher than the upper limitDLIm, on the other hand, the value DLIM is set to the targetdeceleration, in order to restrict the deceleration (step S152). Thedriver presses the snow mode switch on when driving on the road surfacehaving a low friction coefficient, such as the snow-covered road. Abruptbraking during a drive on the road surface of a low friction coefficientmay cause a slip or a skid of the vehicle. When the driver sets the snowmode switch on, the upper limit of deceleration is restricted to apreset value that prevents a possible slip or a skid of the vehicle.

The deceleration restricting process routine is executed repeatedly atpredetermined time intervals. In the case where the snow mode switch ison in the course of the braking control, the restriction of the upperlimit of deceleration is actually implemented at a first timing when thedeceleration restricting process routine is executed after theon-operation of the snow mode switch. In the case where the snow modeswitch is off in the course of the braking control, on the contrary, therestriction of the upper limit of deceleration is cancelled at a firsttiming when the deceleration restricting process routine is executedafter the off-operation of the snow mode switch. The execution of thedeceleration restricting process routine is repeated at relatively shorttime intervals. The time lag between the operation of the snow modeswitch and the restriction of the deceleration or its cancellation isnegligible in the actual state. In the hybrid vehicle of thisembodiment, the operation of the snow mode switch is made effective notonly before the start of braking control but even after the start ofbraking control.

The CPU informs the driver of the restricted setting of the targetdeceleration (step S154), simultaneously with the above processing. Thetechnique adopted in this embodiment flashes the deceleration indicator224 for approximately one second, simultaneously with sounding an alarm.These alarms are given by outputting adequate signals as the alarmsignal and the deceleration indicator signal shown in FIG. 8. Afterrestricting the target deceleration to be not higher than the upperlimit DLIM according to the on-off state of the snow mode switch, theCPU exits from the deceleration restricting process routine and returnsto the deceleration setting process routine of FIG. 17. The CPU displaysthe preset deceleration on the deceleration indicator 224 (see FIG. 7)(step S160), and exits from the deceleration setting process routine.

The detailed process of changing the setting of the target decelerationby the processing discussed above (steps S120 through S140) is describedwith referring to concrete examples of FIGS. 19 through 22. FIG. 19 is atiming chart showing a first example of the setting. In the timing chartof FIG. 19, variations of the on-off state of the Decel switch and theCan-Decel switch, the setting of the target deceleration, the torque ofthe motor 20 to attain the target deceleration, and the position of thechange-speed gear are plotted against the time. The vehicle speed is setto a fixed value in the example of FIG. 19.

The Decel switch is on at a time point al. Although not specificallyshown in the flowchart of FIG. 17, the technique of this embodimentaccepts the change of the setting only when the switch is continuouslyon for a predetermined time period. The CPU inputs the operation of theswitch at step S105 in the deceleration setting process routine (FIG.17), based on the determination of whether or not the switch iscontinuously on for a predetermined time period. Because of thephenomenon called chattering, the on signal and the off signal aredetected alternately at very short cycles when the switch is turned onor off. The structure of accepting the change of the setting after theelapse of the predetermined time period effectively prevents thedeceleration from being significantly changed against the intention ofthe driver due to the chattering.

Accepting the input of the switch after the continuous actuation thereoffor the predetermined time period desirably prevents the setting of thetarget deceleration from being changed when the driver unintentionallytouches the switch. The mechanism of preventing the setting of thetarget deceleration from being changed by an accidental operation of theswitch is especially effective in the structure of the embodiment wherethe Decel switches and the Can-Decel switches are provided on thesteering wheel.

The predetermine time period (hereinafter referred to as the on-decisionreference time) is set as the criterion used to determine whether thedriver operates the switch intentionally or unintentionally. The shorteron-decision reference time heightens the possibility that the setting ofthe target deceleration is changed even by an accidental operation ofthe driver. The longer on-decision reference time, however, worsens theresponse of the Decel switch and the Can-Decel switch. An appropriatevalue is set, for example, experimentally, to the on-decision referencetime by taking into account these conditions. The driver mayalternatively set a desired value to the on-decision reference time.

In the example of FIG. 19, the time period between the time point a1 anda time point a2 exceeds the on-decision reference time. The targetdeceleration is accordingly increased by one step at the time point a2.As described previously with FIG. 11, the technique of the embodimentcarries out the torque control in combination with the changeover of theposition of the change-speed gear, in order to attain an arbitrarydeceleration in a wide range. As clearly shown in the map of FIG. 11,the target deceleration is varied on the large scale by changing overthe position of the change-speed gear and on the fine scale byregulating the motor torque. In this embodiment, the target decelerationis varied stepwise on a relatively fine scale. The variation of thedeceleration at the time point a2 in FIG. 19 is not accompanied with thechangeover of the position of the change-speed gear but is implementedby the regulation of the motor torque. In this example, the fifth speed(5^(th)) is set as the initial position of the change-speed gear.

When the Decel switch is continuously on for a time period between timepoints a3 and a4, which exceeds the on-decision reference time, thetarget deceleration is further increased by another step as shown inFIG. 19. The variation of the deceleration at the time point a4 is alsonot accompanied with the changeover of the position of the change-speedgear but is implemented by the regulation of the motor torque. In thisembodiment, the respective steps of the deceleration are set on the finescale. This widens the possible range of selection on the setting of thetarget deceleration without changing over the position of thechange-speed gear. The driver can thus readily set a desireddeceleration. The motor torque is varied at the time point a4, whereasthe position of the change-speed gear is kept at the fifth speed(5^(th)) as shown in FIG. 19.

In the technique of the embodiment, an operation interval referencetime, which relates to the interval between successive operations of theswitch, as well as the on-decision reference time, is set as thecondition of accepting the input of the switch. In the case ofsuccessive operations of the switch, only when there is a time intervalof or over the operation interval reference time between a firstoperation and a second operation, the second operation is accepted aseffective. The CPU inputs the operation of the switch at step S105 inthe deceleration setting process routine (FIG. 17), based on thedetermination of whether or not the time interval of or over theoperation interval reference time has elapsed since the previousoperation.

In the example of FIG. 19, as the third operation, the Decel switch iscontinuously on for a time period between time points a5 and a6. Thetime period exceeds the on-decision reference time. However, the timeinterval between the second operation and the third operation, that is,the time interval between the time points a4 and a5, is rather short.Here the time interval is shorter than the operation interval referencetime. Although the operation time of the switch exceeds the on- decisionreference time, the third operation is not accepted as effective andchanges none of the setting of the target deceleration, the motortorque, and the position of the change-speed gear.

Using the operation interval reference time effectively prevents thesetting of the target deceleration from being varied in an excessivelyabrupt manner in response to the operation of the driver. When thedriver carries out some operation to vary the deceleration, there isgenerally a certain time delay to the actual speed reduction at thevaried deceleration. If the change of the setting of the targetdeceleration is accepted without the operation interval reference time,there is a possibility that the setting of the target deceleration issuccessively changed without checking the actual decelerations attainedby the successive settings. This may cause the deceleration to be variedsignificantly over the intention of the driver. The arrangement of thisembodiment sets the operation interval reference time, in order toprevent such troubles.

The shorter operation interval reference time does not allow thesufficiently gentle: variation of the setting of the targetdeceleration. The longer operation interval reference time, however,requires an undesirably long time to vary the setting of the targetdeceleration, thereby lowering the controllability. An appropriate valueis set, for example, experimentally, to the operation interval referencetime by taking into account these conditions. The driver mayalternatively set a desired value to the operation interval referencetime.

In the example of FIG. 19, as the fourth operation, the Decel switch iscontinuously on for a time period between time points a7 and a8, whichexceeds the on-decision reference time. The target deceleration isfurther increased in response to the fourth operation. The targetdeceleration is accordingly increased by three steps from the referencelevel prior to any operation of the Decel switch. In this embodiment,the variation in deceleration of this level is not attained only byregulating the motor torque. In response to the fourth operation, theposition of the change-speed gear is thus changed from the fifth speed(5^(th)) to the fourth speed (4^(th)) with the increase of the targetdeceleration. The changeover of the position of the change-speed gear isimplemented according to the map of FIG. 11 as discussed previously.Changing over the position of the change-speed gear to the fourth speed(4^(th)) widens the possible range of deceleration. The motor torque isaccordingly decreased in response to the fourth operation, in order toattain the level of deceleration that is increased by three steps fromthe reference level. The motor torque is specified against the targetdeceleration and the position of the change-speed gear according to themap of FIG. 11.

Changing over the position of the change-speed gear with an increase indeceleration advantageously attains quick acceleration, as well as therequired deceleration. After the braking is performed at a highdeceleration, quick acceleration is generally required to return thevehicle speed to the previous level prior to the braking control.Changing over the position of the change-speed gear to a greater gearratio with an increase in deceleration ensures the quick acceleration atthe changed position of the change-speed gear after the braking control.Changing over the position of the change-speed gear according to thetarget deceleration thus improves the response of the vehicle at thetime of speed reduction and acceleration.

The following description regards an operation to increase thedeceleration. A similar operation is carried out to decrease thedeceleration. In the example of FIG. 19, the Can-Decel switch iscontinuously on as the fifth operation for a time period between timepoints a9 and a10. The time period exceeds the on-decision referencetime. The target deceleration is lowered by one step to the level set atthe time point a4, in response to this operation. The position of thechange-speed gear and the motor torque are simultaneously changed, so asto attain this deceleration.

As the sixth operation, the Can-Decel switch is continuously on for atime period between time points a11 and a12, which is however, shorterthan the on-decision reference time. The sixth operation is accordinglyineffective and does not change the target deceleration, the motortorque, or the position of the change-speed gear. Although notspecifically illustrated in the example of FIG. 19, when the timeinterval between two consecutive operations of the Can-Decel switch isshorter than the operation interval reference time, the second operationis determined to be ineffective and does not change the deceleration orother related factors.

The following describes a second example of the setting of deceleration.FIG. 20 is a timing chart showing the second example of the setting ofdeceleration. In this example, the Decel switch is continuously on for atime period between time points b1 and b2, which exceeds the on-decisionreference time. As described in the first example of the setting, thetarget deceleration is increased by one step in response to thisoperation. The motor torque also increases, in order to attain thetarget deceleration.

The Decel switch is then continuously on as the second operation for atime period between time points b3 and b6, which exceeds the on-decisionreference time. In this case, the Can-Decel switch is also on for a timeperiod between time points b4 and b6, with the operation of the Decelswitch. A time period between the time point b3 at which the operationof the Decel switch starts and the time point b4 at which the operationof the Can-Decel switch starts is shorter than the on-decision referencetime. At the time point b4 when the operation of the Can-Decel switchstarts, the operation of the Decel switch is not accepted as effective.

As described previously in the deceleration setting process routine, theCPU of the control unit 70 does not change the setting of the targetdeceleration in the case of simultaneous operation of the Decel switchand the Can- Decel switch (see step S120 in FIG. 17). In the example ofFIG. 20, although the Decel switch is continuously on for the timeperiod between the time points b3 and b5, which exceeds the on-decisionreference: time, this operation changes none of the target deceleration,the motor torque, and the position of the change-speed gear. This isbecause both the time period while only the Decel switch is operated(the time period between the time points b3 and b4) and the time periodwhile only the Can-Decel switch is operated (the time period between thetime points b5 and b6) are shorter than the on-decision reference time.In one example, if the time period between the time points b3 and b4exceeds the on-decision reference time, the target deceleration isincreased by one step in response to the operation of the Decel switch.In another example, if the time period between the time points b5 and b6exceeds the on-decision reference time, the target deceleration isdecreased by one step in response to the operation of the Can-Decelswitch.

After the elapse of a time interval of or over the operation intervalreference time, the Decel switch is continuously on as the thirdoperation for a time period between time points b7 and b8, which exceedsthe on-decision reference time. The third operation is accepted aseffective and increases the setting of the target deceleration byanother step and the motor torque.

In the second operation discussed above, the operation of the an-Decelswitch starts while the Decel switch is continuously on. n the case ofsimultaneous operation of the Decel switch and the an-Decel switch wherethe Can-Decel switch is operated first, the setting of the targetdeceleration is not changed. In the example of FIG. 20, the Can-Decelswitch is continuously on as the fourth operation for a time periodbetween time points b9 and b11. The Decel switch is also on for a timeperiod between time points b10 and b12, with the operation of theCan-Decel switch. Both the switches are simultaneously on for a timeperiod between the time points b10 and b11. As described previously inthe second operation, the fourth operation changes none of the targetdeceleration, the motor torque, and the position of the change-speedgear.

When the Decel switch and the Can-Decel switch are operatedsimultaneously, the setting of the target deceleration is keptunchanged. This arrangement effectively prevents the target decelerationfrom being changed mistakenly or accidentally against the intention ofthe driver. This arrangement also prevents the setting of the targetdeceleration from being changed frequently at the respective pressingtimings of the Decel switch and the Can-Decel switch.

In the first and the second examples of the setting (FIGS. 19 and 20),the target deceleration is varied in a stepwise manner according to thefrequency of operation of the Decel switch and the Can-Decel switch.This arrangement enables the target deceleration to be varied in a widerange by an operation of a relatively short time, thereby attaining theexcellent controllability. The setting of the target deceleration mayalternatively be varied in a continuous manner according to theoperation time of the switch. The timing chart of FIG. 21 shows a thirdexample of the setting of the target deceleration, which is variedaccording to the operation time.

In this example, the Decel switch is continuously on as the firstoperation for a time period between time points c1 and c3. Like thefirst and the second examples of the setting, the switch operation isaccepted as effective when the time period of the switch operationexceeds the on-decision reference time. In the example of FIG. 21, atime period between the time points c1 and c2 corresponds to theon-decision reference time. In the first operation, the targetdeceleration is increased.in proportion to the operation time of theDecel switch between the time points c2 and b3. The motor torquesimultaneously varies, in order to attain the target deceleration.

When the Decel switch is continuously on as the second operation for atime period between time points c4 and c6, the target deceleration isincreased in proportion to the operation time of the Decel switch afterthe time period c5 when the on-decision reference time has elapsed sincethe start of the operation. The motor torque varies simultaneously withthe increase in deceleration. In the third example of the setting, thetarget deceleration set by the first and the second operations isattained only by varying the motor torque, so that the position of thechange-speed gear is not changed. In the case where the variation intarget deceleration is not attained by only a variation in motor torque,the position of the change-speed gear is changed according to the map ofFIG. 11.

The Decel switch is again continuously on as the third operation for atime period between time points c7 and c8. In this case, the timeinterval between the time point c6 when the second operation isconcluded and the time point c7 when the third operation starts isshorter than the operation interval reference time. As describedpreviously in the first example of the setting, the third operation isnot accepted as effective and does not vary the target deceleration.

As the fourth operation, the Decel switch is continuously on for a timeperiod between time points c9 and c10, which is shorter than theon-decision reference time. The fourth operation is accordingly notaccepted as effective and does not vary the target deceleration.

In the third example of the setting, like the case of increasing thetarget deceleration, the target deceleration is decreased according tothe operation time of the Can-Decel switch. When the Can-Decel switch iscontinuously on as the fifth operation for a time period between timepoints c11 and c13, the target deceleration is decreased in proportionto the operation time of the Can-Decel switch after the time period c12when the on-decision reference time has elapsed.

As the sixth operation, the Can-Decel switch is continuously on for atime period between time points c14 and c15, which is shorter than theon-decision reference time. The fourth operation is accordingly notaccepted as effective and does not vary the target deceleration.

The arrangement of varying the target deceleration continuouslyaccording to the operation time of the switch as described in the thirdexample of the setting enables the driver to obtain the desireddeceleration without operating the switch many times. The continuousvariation in target deceleration ensures the minute regulation of thetarget deceleration according to the intention of the driver. Althoughthe target deceleration is varied in proportion to the operation time ofthe switch in the third example of the setting, the target decelerationmay be varied non-linearly relative to the operation time of the switch.One available process varies the target deceleration by a gentle slopeat the beginning of the operation of the switch and by a more abruptslope with an increase in operation time.

The timing chart of FIG. 22 shows a fourth example of the setting, wherethe target deceleration enters a rejection range. In this example, theDecel switch is continuously on as the first operation for a time periodbetween time points d1 and d3. The operation of the Decel switch isaccepted as effective at a time point d2 when the on-decision referencetime has elapsed since the start of the operation. The first operationaccordingly increases the target deceleration by one step and raises themotor torque.

When the Decel switch is continuously on again as the second operationfor a time period between time points d4 and d6, the operation of theDecel switch is accepted as effective at a time point d5 when theon-decision reference time has elapsed. The second operation increasesthe target deceleration by another step and raises the motor torque.

The Decel switch is continuously on again as the third operation for atime period between time points d7 and d9. The operation of the Decelswitch is accepted as effective at a time point d8 when the on-decisionreference time has elapsed. The third operation also increases thetarget deceleration. In the case where the upper limit of the targetdeceleration is not set, the target deceleration is increased by onestep as shown by the one-dot chain line in FIG. 22. In this case, likethe first example of the setting (FIG. 19), the operation requires notonly a variation in motor torque but a change in position of thechange-speed gear as shown by the one-dot chain lines.

In the fourth example of the setting, however, the upper limit of thetarget deceleration is restricted to a value DClim. Varying the targetdeceleration to the value defined by the one-dot chain line in responseto the third operation makes the target deceleration exceed the upperlimit DClim. In this case, the target deceleration enters the rejectionrange. As described previously (see step S150 in the flowchart of FIG.17), the target deceleration is restricted to the upper limit DClim,that is, a value defined by the solid line in FIG. 22. This alsorequires a variation in motor torque and a change in position of thechange-speed gear respectively defined by the solid line. In the exampleof FIG. 22, the motor torque is higher than the level before therestriction, while the position of the change-speed gear maintains thefifth speed (5^(th)). This is based on the map of FIG. 11, in order toattain the deceleration DClim. The position of the change-speed gear andthe motor torque after the restriction are, however, not limited to suchvariations.

As described above with some concrete examples, in the hybrid vehicle ofthis embodiment, the driver operates the Decel switch and the Can-Decelswitch to set the desired deceleration. The arrangement of theembodiment effectively prevents the deceleration from being variedaccidentally or extremely frequently against the intention of thedriver.

After the conclusion of the deceleration setting process routine, theprogram returns to the speed reduction control routine (FIG. 15). TheCPU determines whether or not the accelerator pedal is off, at thecriterion of performing the power-source braking control (step S200).The determination is based on the input signal regarding the travel ofthe accelerator pedal (see FIG. 8). In the case where the acceleratorpedal is not off, it is not the state of performing the power-sourcebraking control. The CPU thus exits from the speed reduction controlroutine without any further processing.

In the case where the accelerator pedal is off, the CPU subsequentlydetermines whether or not the E position braking control is allowed(step S205). As described previously in the deceleration setting processroutine (FIG. 17), in the case of the switch failure, the prohibitionflag is set to prohibit the E position braking control (step S180 inFIG. 17). When the prohibition flag is set, the CPU determines that theE position braking control is not allowed. The E position brakingcontrol is also not allowed when the gearshift lever is not in the Eposition.

When it is determined at step S205 that the E position braking controlis not allowed, the CPU carries out the standard braking control andsets a predetermined negative value Tm0 to the target torque of themotor 20 (step S210). The predetermined value Tm0 is arbitrarily setwithin the range of the rated torque of the motor 20. In thisembodiment, the predetermined value Tm0 is set to a level that ensures asufficient deceleration at the D position by the power-source braking.

When it is determined at step S205 that the E position braking controlis allowed, on the other hand, the CPU carries out the E positionbraking control. The concrete procedure of the E position brakingcontrol first selects the position of the change-speed gear (step S215)according to the procedure of FIG. 23.

FIG. 23 is a flowchart showing a routine of the change-speed gearposition selection process. In the change-speed gear position selectionroutine, the CPU determines whether or not the E position has just beenselected (step S220). Like step S20 in the initial setting processroutine (FIG. 16), it is determined whether or not the gearshiftposition has just been changed from the D position to the E position.The term ‘just’ implies a time interval between the change of thegearshift position to the E position and the variation in setting of thetarget deceleration.

When it is determined that the E position has just been selected, theCPU subsequently determines whether or not a preset deceleration isattained at the position of the change-speed gear used in the D position(step S222). As described previously in the initial setting processroutine (FIG. 16), when the gearshift position has just been changedfrom the D position to the E position, the position of the change-speedgear used in the D position is set to the initial position of thechange-speed gear. The CPU accordingly determines whether or not thepreset deceleration is attained at the initial position of thechange-speed gear at step S222. In the case of an affirmative answer atstep S222, the CPU sets the initial position of the change-speed gear,that is, the position of the change-speed gear used in the D position,to the current position of the change-speed gear (step S224). The presetdeceleration means the required minimum deceleration as describedpreviously. If the maximum deceleration attained at the position of thechange-speed gear used in the D position is not lower than the presetdeceleration, the CPU determines at step S222 that the presetdeceleration is attained at the position of the change-speed gear usedin the D position.

When it is determined at step S220 that the E position has just not beenselected or when it is determined at step S224 that the presetdeceleration is not attained at the position of the change-speed gearused in the D position, the position of the change-speed gear is setaccording to the map of FIG. 11. In this case, the CPU refers to the mapand determines whether or not there are a plurality of differentpositions of the change-speed gear mapped to the preset targetdeceleration (step S226). In the case where there is only one positionof the change-speed gear mapped to the preset deceleration, the positionof the change-speed gear read from the map is set to the currentposition of the change-speed gear step S228).

In the case where there are two different positions of the change-speedgear mapped to the preset deceleration, on the other and, the CPUcompares the remaining charge SOC of the battery 50 with a predeterminedvalue H (step S230). As described previously with the map of FIG. 13,there are two different decelerations attained at each position of thechange-speed gear, that is, the deceleration by the regenerativeoperation of the motor 20 and the deceleration by the power operation ofthe motor 20. When there are two different positions of the change-speedgear mapped to the preset deceleration, the preset deceleration isattained by the regenerative operation of the motor 20 at one positionof the change-speed gear, while being attained by the power operation ofthe motor 20 at the other position of the change-speed gear. In the casewhere there are two different positions of the change-speed gear mappedto the preset deceleration, the appropriate position of the change-speedgear is selected according to the remaining charge SOC of the battery50.

When the remaining charge SOC of the battery 50 is not less than thepredetermined value H, it is desirable to consume the electric poweraccumulated in the battery 50, in order to prevent the battery 50 frombeing excessively charged. The CPU accordingly selects the position ofthe change-speed gear that attains the preset deceleration by the poweroperation of the motor 20, that is, the position of the change-speedgear having a larger gear ratio out of the two alternatives (step S232).When the remaining charge SOC of the battery 50 is less than thepredetermined value H, on the other hand, it is desirable to charge thebattery 50. The CPU accordingly selects the position of the change-speedgear that attains the preset deceleration by the regenerative operationof the motor 20, that is, the position of the change-speed gear having asmaller gear ratio out of the two alternatives (step S234). In order toprevent the position of the change-speed gear from being frequentlyswitched over between the two alternatives according to the remainingcharge SOC, it is desirable to set a certain hysteresis for thedetermination of step S230.

When the appropriate position of the change-speed gear is selected, theprogram returns to the speed reduction control routine. The CPU thenactually changes over the position of the change-speed gear (step S240).The actual changeover of the position of the change-speed gear isimplemented by outputting an appropriate signal to the transmissioncontrol signal (see FIG. 8) and controlling the on and off conditions:of the clutches and the brakes included in the transmission 100according to the table of FIG. 3, based on the selected position of thechange-speed gear.

After the position of the change-speed gear has actually been changed,the CPU calculates the target torque to be output from the motor 20(step S245). The total torque to be output from the engine 10 and themotor 20 functioning as the power source is calculated from the presetdeceleration, that is, the torque to be output to the axle 17, at theselected position of the change-speed gear according to Equations (2)through (6) with the gear ratios k1 through k5. The braking force outputfrom the engine 10, that is, the power of the engine brake, issubstantially unequivocally determined according to the revolving speedof the crankshaft 12. The torque to be output from the motor 20 is thusobtained by subtracting the torque by the engine brake from the totaltorque to be output from the power source.

In this embodiment, the target torque of the motor 20 is calculated inthe above manner. A map for specifying the target torque of the motor 20may alternatively be provided with the map of FIG. 11. Another possibleprocedure measures the deceleration of the vehicle with an accelerationsensor and feedback controls the torque of the motor 20, in order toattain the preset deceleration. Although the calculation of the motortorque is performed after the actual changeover of the position of thechange-speed gear in the flowchart of FIG. 15, this is just forconvenience of illustration. The calculation may thus be performedsimultaneously with the actual changeover of the position of thechange-speed gear.

The above processing causes the target torque of the motor 20 to be setunder the standard braking control or under the E position brakingcontrol. The CPU then carries out a braking control (step S250), so asto control the operations of the motor 20 and the engine 10. The CPUstops the fuel injection to the engine 10 and the ignition, in order toapply the engine brake. The CPU may simultaneously control the VVTmechanism incorporated in the engine 10. Since the braking force by thepower-source braking can be regulated by the torque of the motor 20, theprocedure of this embodiment does not control the VVT mechanism here.

The motor 20 is driven by the PWM control. The CPU sets a voltage to beapplied to the coils on the stator 24 in the motor 20. The voltage isdetermined corresponding to the revolving speed and the target torque ofthe motor 20, based on a preset table. In the case of the regenerativeoperation of the motor 20, a negative value is set to the voltage. Inthe case of the power operation of the motor 20, on the contrary, apositive value is set to the voltage. The CPU controls the on-offconditions of the respective transistors included in the driving circuit40, in order to cause the preset voltage to be applied to the coils. ThePWM control is a known technique and is thus not described in detailhere.

The hybrid vehicle of the embodiment repeatedly carries out the speedreduction control routine discussed above, so as to implement thebraking control by the power source braking. The hybrid vehicle may alsocarry out the braking control by the wheel braking in combination withthe braking control by the power source braking.

The hybrid vehicle of the embodiment changes over the position of thechange-speed gear in the transmission 100 according to the map shown inFIG. 11, while controlling the torque of the motor 20, thereby attainingthe braking control at the desired deceleration corresponding to theinstruction of the driver in a wide range. The arrangement enables thebraking and acceleration of the vehicle to be carried out with theminimum frequency of the change of the foot position between theaccelerator pedal and the brake pedal, thus significantly improving thecontrollability of the vehicle.

Applicability of the power-source braking in a wide range enables thekinetic energy of the vehicle to be recovered efficiently, thusimproving the energy efficiency of the vehicle.

The hybrid vehicle of the embodiment carries out the restriction of thedeceleration set by the driver in the snow mode. This effectivelyprevents the driver from setting the higher deceleration than requiredand thus prevents a slip or a skid of the vehicle due to the braking atthe high deceleration on the road surface having a relatively smallfriction coefficient, such as the snow-covered road. This arrangementensures the sufficient driving stability of the vehicle. Thisarrangement also enables the driver to vary the setting of the targetdeceleration without the fear of a skip or a skid of the vehicle, thusimproving the controllability of the vehicle.

In the hybrid vehicle of the embodiment, the snow mode switch is locatednear the gearshift lever (see FIG. 4). The gearshift lever is disposedat a specific position that ensures the easy operation thereof.Positioning the snow mode switch near the gearshift lever accordinglyensures the excellent controllability for the driver. The snow modeswitch may, however, be arranged on the gearshift lever, on the steeringwheel, or at any suitable place.

The hybrid vehicle of the embodiment displays the restricteddeceleration, that is, the fact that the deceleration set by the drivercan not be attained, when the upper limit of the deceleration isrestricted to the predetermined level. The driver can thus continuouslydrive the vehicle without feeling any incompatibility with regard to thedeceleration attained and without having the fear of a possible failure.

In the hybrid vehicle of the embodiment, the map (FIG. 11) is specifiedto make two different positions of the change-speed gear mapped to eachpreset deceleration. Among the two positions of the change-speed gear,one corresponds to the regenerative operation of the motor 20 and theother corresponds to the power operation of the motor 20. Suchspecification of the map enables the hybrid vehicle of the embodiment toselect an appropriate position of the change-speed gear according to theremaining charge SOC of the battery 50, so as to actuate the powersource braking to brake the vehicle. This arrangement enables the hybridvehicle of the embodiment to utilize the power source braking,irrespective of the remaining charge SOC of the battery 50, therebyattaining a drive of excellent operatability.

A4. First Modification of First Embodiment

When the snow mode switch is on, the embodiment carries out thedeceleration restricting process to restrict the deceleration not to behigher than the predetermined upper limit (see the flowchart of FIG.18). A variety of other technique are applicable to restrict thedeceleration. FIG. 24 is a flowchart showing another decelerationrestricting process routine as one modification. In this modifiedprocedure, the CPU detects the driving state of the vehicle andrestricts the deceleration, irrespective of the on-off state of the snowmode switch.

When the program enters the deceleration restricting process routine ofFIG. 24, the CPU first inputs numbers of rotations NWR and NWL of thedriving wheels 18R and 18L (step S302). As described previously in FIG.8, the numbers of rotations of the left and right driving wheels 18L and18R are input to calculate the vehicle speed. The CPU separately inputsthe respective numbers of rotations at step S302.

The CPU then calculates the absolute value of the difference between thenumbers of rotations NWL and NWR and compares the absolute value with apredetermined reference value SLIP (step S304). The predeterminedreference value SLIP is used as the criterion of the determination ofwhether or not a slip occurs on the driving wheels 18L and 18R. In thecase of no slip, the number of rotations of the left driving wheel 18Lis substantially coincident with the number of rotations of the rightdriving wheel 18R. When the vehicle changes the traffic lane, thedifference in diameter of the inner ring causes a slight differencebetween the numbers of rotations of the left and right driving wheels18L and 18R. In the case of a slip, there is a significantly largedifference between the numbers of rotations of the left and rightdriving wheels 18L and 18R. The reference value SLIP is accordingly setto be greater than the possible difference between the numbers ofrotations occurring when the driver changes the lane but to be smallerthan the possible difference between the numbers of rotations occurringat the time of a slip.

When it is determined that the absolute value of the difference betweenthe numbers of rotations NWL and NWR of the driving wheels 18L and 18Ris not greater than the predetermined reference value SLIP, there is nooccurrence of the slip. The CPU accordingly exits from the decelerationrestricting process routine without any further processing. When it isdetermined that the absolute value of the difference between the numbersof rotations NWL and NWR of the driving wheels 18L and 18R is greaterthan the predetermined reference value SLIP, on the other hand, there isoccurrence of the slip. The CPU accordingly subtracts a predeterminedvalue ΔDC from the preset deceleration (step S306), and informs thedriver of the restricted setting of the deceleration (step S308). Thesame technique as described in the embodiment (see step S154 in theflowchart of FIG. 18) is applicable to display the restricteddeceleration.

After the restriction of the deceleration, the CPU again reads thenumbers of rotations NWR and NWL of the driving wheels 18R and 18L (stepS302) and determines the occurrence or non-occurrence of a slip (stepS304). The preset deceleration is successively decreased by thepredetermined value ΔDC until there is no occurrence of a slip.

The restriction of the deceleration by the feedback control effectivelyprevents the occurrence of a slip or a skid of the vehicle. In thestructure of the embodiment (FIG. 18), the deceleration is restricted tothe predetermined upper limit that has an extremely low probability ofcausing a slip. This, however, means that there is still a very littlepossibility of causing a slip. The modified procedure of FIG. 24, on theother hand, ensures the perfect prevention of the occurrence of a slipand thereby further improves the driving stability of the vehicle. Themodified procedure gradually lowers the deceleration until there is nooccurrence of a slip. This arrangement effectively prevents the possiblesetting range of the deceleration from being narrowed unnecessarily.Although the procedure of FIG. 24 successively decreases the setting ofthe deceleration by the predetermined value ADC, the predetermined valuemay not be fixed but be varied according to any suitable techniqueadopted in the feedback control.

The deceleration restricting process routine of the modified proceduremay be used in place of the deceleration restricting process routine ofthe embodiment (FIG. 18), or together with the routine of theembodiment. In the latter case, the deceleration can be restricted,based on both the requirement of the driver and the detected drivingstate of the vehicle. This further improves the driving stability of thevehicle.

A variety of other techniques may be applied to restrict thedeceleration. FIG. 25 is a graph showing another process of restrictingthe deceleration, or more specifically showing a stepwise variation ofthe deceleration in response to the operation of the Decel switch, withthe deceleration as ordinate and the frequency of operations of theDecel switch as abscissa. When the deceleration is not restricted, thedeceleration increases to a level corresponding to a point P1 by a firstoperation of the Decel switch, to a point P3 by a second operation, to apoint P4 by a third operation, and to a point P7 by a fourth operationas shown by a plot LL1 of the solid line.

A plot LL2 of the dashed line represents the case where the upper limitof deceleration is restricted as discussed in the above embodiment. Theupper limit of deceleration is set to a point P5 in the ON position ofthe snow mode switch. The deceleration should originally be increased tothe point P4 and the point P7 by the third and the fourth operations ofthe Decel switch. When the deceleration restricting process is carriedout, however, the upper limit of deceleration is restricted to the pointP5. The deceleration accordingly varies as shown by the plot LL2 of thedashed line.

The upper limit of deceleration may alternatively be restricted bylowering the rate of increase of the deceleration by each operation ofthe Decel switch. A plot LL3 of the one-dot chain line represents avariation in deceleration when this technique is adopted. In thistechnique, in the ON position of the snow mode switch, the decelerationincreases to a level corresponding to a point P2, which is lower thanthe level of the standard deceleration plot LL1, by the first operationof the Decel switch, to the point P1 by the second operation, to a pointP6 by the third operation, and to the point P7 by the fourth operation.The four successive operations of the Decel switch set the decelerationto the level corresponding to the point P7 in the OFF position of thesnow mode switch, but restrict the deceleration to the lower levelcorresponding to the point P3 in the ON position of the snow modeswitch. In the graph of FIG. 25, for the simplicity of illustration, theupper limit of the plot LL2 is set to be different from the upper limitof the plot LL3.

The above description regards the restricting process in the case wherethe deceleration varies in a stepwise manner. The similar process is,however, applicable to the case where the deceleration varies in acontinuous manner. In this case, the upper limit of deceleration may berestricted simply to a preset level. A gentler slope may alternativelybe set to the variation in deceleration by each operation of the switch,in order to restrict the upper limit of deceleration. Although the upperlimit of deceleration is set to a fixed value in the above description,the upper limit may be varied in a stepwise manner in response to theoperation of the driver or according to the driving state of thevehicle.

The above embodiment and its modified example regard the case where theupper limit of deceleration is restricted. The principle of the presentinvention is, however, applicable to the case where the lower limit ofdeceleration is restricted. For example, when the vehicle runs withrelatively narrow distances from adjacent vehicles on the same trafficlane, it is desirable to keep a certain level of deceleration, in orderto assure a sufficient interval between vehicles. In such cases, forexample, the driver operates a switch similar to the snow mode switch(see FIG. 4), so as to restrict the lower limit of deceleration to benot less than a predetermined level. In a vehicle with a sensor thatmeasures distances from adjacent vehicles by utilizing radio wave orlaser, the feedback control is carried out to vary the lower limit ofdeceleration, in order to assure the interval of or over a presetdistance.

The above embodiment and its modified example regard the case in whichthe possible setting range of the deceleration is narrowed in responseto the operation of the snow mode switch. The principle of the presentinvention is also applicable to the case in which the possible settingrange of the deceleration is widened under predetermined conditions. Byway of example, in the graph of FIG. 25, it is assumed that the plot LL2of the dashed line represents a normal possible setting range of thedeceleration. In response to a driver's operation of a certain switch,the possible setting range of the deceleration may be widened to thelevel defined by the plot LL1 of the solid line.

A5. Second Modification of First Embodiment

The first embodiment regards the case where two different positions ofthe change-speed gear are mapped to a deceleration corresponding to acertain vehicle speed. One of the two positions of the change-speed gearcorresponds to the regenerative operation of the motor 20, whereas theother corresponds to the power operation of the motor 20. The principleof the present invention is, however, not restricted to this arrangementbut may be applied to another arrangement where three or more differentpositions of the change-speed gear are mapped to a preset deceleration.The present invention is also applicable to still another arrangementwhere all the positions of the change-speed gear correspond to eitherone of the regenerative operation and the power operation of the motor20.

FIG. 26 is a modified example of the map showing the combinations of thevehicle speed, the deceleration, and the position of the change-speedgear. In this modification, for example, three different positions ofthe change-speed gear, that is, third speed (3^(rd)) through fifth speed(5^(th)), are mapped to a certain deceleration defined by an area A inFIG. 26.

FIG. 27 shows the revolving speed of the power source, the engine brake,and the regenerative torque at the respective positions of thechange-speed gear to attain the deceleration shown by the area A. Underthe condition of a fixed vehicle speed, that is, a fixed rotating speedof the axle 17, the revolving speed of the motor 20 and the engine 10functioning as the power source decreases with a shift of thechange-speed gear position from the third speed (3^(rd)) to the fifthspeed (5^(th)). Although the revolving speed decreases at a fixedproportion in FIG. 27, the variation in revolving speed actually dependsupon the gear ratio attained at each position of the change-speed gear.

With a variation in revolving speed of the engine 10, the braking forceby the engine brake varies. The middle graph of FIG. 27 shows avariation in braking force by the engine brake against the position ofthe change-speed gear. The braking force by the engine brake is loweredwith the shift of the position of the change-speed gear from the thirdspeed (3^(rd)) to the fifth speed (5^(th)) and the resulting decrease inrevolving speed.

The decrease in braking force by the engine brake raises the brakingtorque of the motor 20 required to attain the deceleration defined bythe area A shown in FIG. 26. The lower graph of FIG. 27 shows avariation in regenerative torque. In this modified example, the motor 20carries out the regenerative operation at all the positions of thechange-speed gear from the third speed (3^(rd)) to the fifth speed(5^(th)). The setting may, however, be changed to make the third speed(3^(rd)) correspond to the power operation of the motor 20. In the casewhere there are three or more different positions of the change-speedgear mapped to a preset deceleration as discussed above, the respectivepositions of the change-speed gear have different quantities ofregenerated electric power.

FIG. 28 is a flowchart showing another change-speed gear positionselection routine executed in this modified example. In the modifiedexample, the processing of and after step S226 in the change-speed gearposition selection routine (FIG. 23) discussed previously is replaced bythis series of processing. The CPU refers to the map shown in FIG. 26and determines whether or not there is only one position of thechange-speed gear mapped to the preset target deceleration (step S226′).In the case where the preset deceleration is attained at only oneposition of the change-speed gear, the position of the change-speed gearread from the map of FIG. 26 is set to the current position of thechange-speed gear (step S228′).

In the case where there are a plurality of different positions of thechange-speed gear mapped to the preset deceleration, the CPU thendetermines whether the preset deceleration is attained at two differentchange-speed gear positions or more (step S227). When it is determinedthat there are two different positions of the change-speed gear mappedto the preset deceleration, the CPU refers to the remaining charge SOCof the battery 50 and compares the remaining charge SOC with apredetermined value H (step S230). In the case where the remainingcharge SOC is not less than the predetermined value H, the CPU selectsthe position of the change-speed gear having the lesser quantity ofregenerated electric power, that is, the position of the change-speedgear having a larger gear ratio out of the two alternatives (step S232),with a view to preventing the battery 50 from being excessively charged.In the case where the remaining charge SOC is less than thepredetermined value H, on the other hand, the CPU selects the positionof the change-speed gear suitable for charging the battery 50, that is,the position of the change-speed gear having a smaller gear ratio out ofthe two alternatives (step S234). This series of the processing isidentical with the processing described previously in the embodiment(FIG. 23).

When it is determined that there are more than two different positionsof the change-speed gear, that is, there are three different positionsof the change-speed gear, mapped to the preset deceleration, the CPUcompares the remaining charge SOC of the battery 50 with twopredetermined threshold values H1 and H2 (step S236). A relationshipH1<H2 holds between these threshold values. In the case where theremaining charge SOC is not less than the threshold value H2, the CPUselects the position of the change-speed gear most suitable forcharging, that is, the position of the change-speed gear having alargest gear ratio (step S237). In the case where the remaining chargeSOC is less than the threshold value H2 but is not less than thethreshold value HI, the CPU selects the position of the change-speedgear having an intermediate gear ratio out of the three alternatives(step S238). In the case where the remaining charge SOC is less than thethreshold value HI, the CPU selects the position of the change-speedgear having the least quantity of regenerated electric power, that is,the position of the change-speed gear having a smallest gear ratio (stepS239).

The threshold values H1 and H2 used for the decision at step S236 arecriteria to change over the position of the change-speed gear.Appropriate values are set to the threshold values H1 and H2, so thatthe optimum position of the change-speed gear having the desiredquantity of regenerated electric power is selected corresponding to thecharge level of the battery 50. Both the threshold values H1 and H2 maybe different from the reference value HL used at step S230, oralternatively either one of the threshold value H1 and H2 may becoincident with the reference value HL. In the change-speed gearposition selection routine of the modified example, it is also desirableto set certain hystereses for the decisions of steps S230 and S236, inorder to prevent the position of the change-speed gear from beingfrequently switched over between and among the alternatives according tothe remaining charge SOC.

Setting the map (FIG. 26) to allow selection among the three or moredifferent positions of the change-speed gear advantageously enables thecharge level of the battery to be regulated minutely. In the modifiedexample discussed above, the regenerative braking control is carried outin the range of the third speed (3^(rd)) to the fifth speed (5^(th)).The map may, however, be set to cause the motor 20 to carry out thepower operation at all the positions of the change speed gear. The mapmay alternatively be set to cause the motor 20 to carry out either theregenerative operation or the power operation in the adopted range ofthe change-speed gear position.

In the embodiment.and its modified example discussed above, when thereare a plurality of different positions of the change-speed gear mappedto a target deceleration, the optimum position of the change-speed gearis selected, based on the remaining charge SOC of the battery 50. Thetechnique of the present invention is, however, applicable to otherarrangements of selecting the position of the change-speed gear based,on a diversity of other conditions. For example, in the change-speedgear position selection routine, preference may be given to the previousposition of the change-speed gear selected for a previous drive. Suchpreference effectively reduces a possible shock due to the changeover ofthe position of the change-speed gear in the braking process by thepower source braking. In a vehicle that enables the position of thevehicle to be verified in topography, the change-speed gear positionhaving the larger gear ratio may be selected while the vehicle runs onan upward slope. This ensures smooth acceleration subsequent to braking.The optimum position of the change-speed gear may be selected, based onany combination of these diversity of conditions.

A6. Third Modification of First Embodiment

The above embodiment regards the parallel hybrid vehicle in which theengine 10 is directly linked with the motor 20 and connected with theaxle 17 via the transmission 100. The principle of the present inventionis, however, applicable to any parallel hybrid vehicles of variousconfigurations, in which the output from the engine is directlytransmittable to the axle. The present invention is further applicableto series hybrid vehicles of various configurations, in which the outputof the engine is not directly transmitted to the drive shaft but is usedonly for power generation.

FIG. 29 shows the structure of such a series hybrid vehicle. In theseries hybrid vehicle, a motor 20A as the power source is connected withan axle 17A via a torque converter 30A and a transmission 100A. Anengine 10A is not connected with the axle 17A but is linked with agenerator G. The motor 20A is connected to a battery 50A via a drivingcircuit 40A. The generator G is connected with the battery 50A via adriving circuit 41. The driving circuits 40A and 41 are constructed astransistor inverters like the driving circuit 40 discussed in the aboveembodiment. The operations of these driving circuits 40A and 41 arecontrolled by a control unit 70A.

In the series hybrid vehicle of the above structure, the power outputfrom the engine 10A is converted to electric power by means of thegenerator G. The electric power is accumulated in the battery 50A andalso used to drive the motor 20A. The vehicle is driven by the power ofthe motor 20A. The motor 20A outputs a negative torque as the brakingforce, so as to apply the power-source braking. Like the parallel hybridvehicle of the embodiment, the series hybrid vehicle of this modifiedstructure having the transmission 100A carries out the braking:controlby the combination of the torque of the motor 20A with the position ofthe change-speed gear, so as to attain the deceleration set by thedriver in a wide range.

In the hybrid vehicle of the embodiment, the target torque of the motor20 is calculated by subtracting the braking torque by engine brake fromthe total torque to be output to the axle 17. In the hybrid vehicle ofthe modified structure, the braking force by engine brake is equal tozero, so that the braking torque to be output to the axle 17A iscoincident with the target torque of the motor 20A.

The embodiment described above uses the transmission 100 that changesthe gear ratio in a stepwise manner. The transmission 100 may have anyother suitable structure, for example, a mechanism of continuouslyvarying the gear ratio.

The principle of the present invention is applicable to a vehicle usingonly the motor as the power source. The structure of such a vehiclecorresponds to the structure of the series hybrid vehicle shown in FIG.29 without the engine 10A, the generator G, and the driving circuit 41.In this vehicle, in the same manner as the parallel hybrid vehicle ofthe embodiment and the series hybrid vehicle of FIG. 29, controlling thetorque of the motor 20A linked with the axle and the position of thechange-speed gear attains the target deceleration set by the driver in awide range. Although the driver sets the target deceleration in theabove embodiment, the driver may set another speed reduction rate, suchas the braking force or the quantity of braking applied to the wheels.

B. Second Embodiment

B1. Structure of Apparatus

The following describes a second embodiment according to the presentinvention. The hybrid vehicle of the second embodiment has a similarhardware configuration to that of the first embodiment, except astructure in the vicinity of a gearshift lever. FIG. 30 shows anoperation unit 160 for selecting the gearshift position in the hybridvehicle of the second embodiment. The operation unit 160 is locatedalong a longitudinal axis of the vehicle on the floor next to thedriver's seat.

As shown in FIG. 30, the operation unit 160 includes a gearshift lever162. The driver slides the gearshift lever 162 along the longitudinalaxis of the vehicle, so as to select one among available gearshiftpositions. The available gearshift positions include a parking (P)position, a reverse (R) position, a neutral (N) position, a drive (D)position, a fourth position (4), a third position (3), a second position(2), and a low position (L), which are arranged in this order from theforward of the vehicle.

The operation unit 160 for selecting the gearshift position also has aslide knob 161 as a mechanism of setting the deceleration. The driverslides the slide knob 161 along the longitudinal axis of the vehicle toset the deceleration. The driver shifts the slide knob 161 forward tocontinuously increase the deceleration, while shifting the slide knob161 backward to continuously decrease the deceleration. The setting ofthe deceleration using the slide knob 161 is carried out, irrespectiveof the current gearshift position of the gearshift lever 162. The shiftof the slide knob 161 in the deceleration-increasing direction enhancesthe power source braking in a stepwise manner. The shift of the slideknob 161 in the deceleration-decreasing direction weakens the powersource braking in a stepwise manner.

The structure of this embodiment enables the driver to manually changeover the position of the change-speed gear. Selection between anautomatic changeover mode and a manual changeover mode is implemented byan operation of the gearshift lever 162. As shown in FIG. 30, thegearshift lever 162 of this embodiment is not only slide along thelongitudinal axis of the vehicle to select the gearshift position but isslid horizontally at the drive (D) position. The position selected bythe horizontal slide is referred to as an M position. While thegearshift lever 162 is at the M position, the manual changeover mode isselected to allow manual changeover of the change-speed gear position.While the gearshift lever 162 is located at any other positions, theautomatic changeover mode is selected to automatically change over theposition of the change-speed gear. Not the gearshift lever 162 butswitches provided on the steering wheel are used for the manualchangeover of the change-speed gear position as discussed later. Thestructure of the first embodiment shown in FIG. 5 may be applied forgearshift position UP and DOWN switches.

The operation unit 160 includes a sensor for detecting the gearshiftposition and an M position switch, which is on when the gearshift lever162 is at the M position. Signals from these sensor and switch aretransmitted to the control unit 70 and used for a diversity of controlprocesses executed in the vehicle as discussed later.

Like the hybrid vehicle of the first embodiment, the hybrid vehicle ofthe second embodiment varies the deceleration at each position of thechange-speed gear by regulating the torque of the motor 20. FIG. 31 is agraph showing a variable range of the deceleration at each position ofthe change-speed gear in the hybrid vehicle of the second embodiment.The deceleration attained at each position of the change-speed gear isvaried by regulating the torque of the motor 20. At the second speed(2^(nd)), the deceleration is varied in a range defined by theshort-dashed lines. The decelerations at the third speed (3^(rd)), atthe fourth speed (4^(th)), and at the fifth speed (5^(th)) arerespectively varied in a range defined by the solid lines, in a rangedefined by the one-dot chain lines, and in a range defined by thelong-dashed lines.

The driver operates the slide knob 163 to set the deceleration of thevehicle. In this embodiment, the deceleration may be set continuously ina range of a straight line BL to a straight line BU. The possiblesetting range of the deceleration by the driver depends upon thegearshift position. For example, when the gearshift position is at thethird (3) position, the deceleration may be set in a range using up tothe third speed (3^(rd)), that is, a range of a straight line B3 to thestraight line BU. The technique of the second embodiment reads the gearratio attaining the deceleration set by the driver against the vehiclespeed in the map of FIG. 31 and carries out the braking control.

B2. Drive Control Process:

In the hybrid vehicle of the second embodiment, the control unit 70executes a drive control process discussed below and controls theoperations of the engine 10 and the motor 20, so as to enable thedriving discussed above. FIG. 32 is a flowchart showing a drive controlroutine executed in the second embodiment. This series of the processingis executed at preset time intervals by the CPU in the control unit 70.

When the program enters the routine, the CPU first carries out achange-speed gear position setting process (step S510). FIG. 33 is aflowchart showing a routine of the change-speed gear position settingprocess. When the program enters the change-speed gear position settingprocess routine, the CPU first receives signals from various switchesand the vehicle speed (step S515). The signals directly relating to thechange-speed gear position setting process routine include the signalrepresenting the gearshift position, the signal of the M positionswitch, and the signals of the UP and DOWN switches.

The CPU then determines whether or not the current gearshift position isthe M position, in response to the input signal (step S520). Thedecision is based on the on-off state of the M position switch.

In the case where the current gearshift position is other than the Mposition, the position of the change-speed gear is set according to thecurrent gearshift position and the vehicle speed (step S525). In thecase of the gearshift position other than the position M, after settingthe change-speed gear position according to the current gearshiftposition and the vehicle speed, the CPU exits from the change-speed gearposition setting process routine.

In the case where the current gearshift position is the M position, onthe other hand, the CPU turns on an M position indicator (step S530). Inparallel with this processing, the CPU sets the position of thechange-speed gear in response to the operations of the UP and DOWNswitches. The CPU determines whether or not the UP switch is in ONposition (step S535). When the UP switch is in the ON position, the CPUraises the current setting of the change-speed gear position by one step(step S540). The increase in setting of the change-speed gear positionmeans that the setting of the change-speed gear position is changed to ahigher speed having a higher number allocated thereto, that is, thespeed having a smaller gear ratio. The transmission 100 of the secondembodiment does not have higher speeds than the fifth speed (5^(th)) forthe available position of the change-speed gear. The raise in setting atstep S35 is accordingly performed in the range up to the fifth speed(5^(th)). After the position of the change-speed gear reaches the fifthspeed (5^(th)), any further on operation of the UP switch does notchange the setting of the change-speed gear position.

When it is determined at step S535 that the UP switch is not in the ONposition, the CPU subsequently determines whether or not the DOWN switchis in ON position (step S545). When the DOWN switch is in the ONposition, the CPU lowers the current setting of the change-speed gearposition by one step (step S550). The reduction in setting of thechange-speed gear position means that the setting of the change-speedgear position is changed to a lower speed having a lower numberallocated thereto, that is, the speed having a larger gear ratio. Thereduction in setting at step S550 is performed in the range down to thefirst speed (L). After the position of the change-speed gear reaches thefirst speed (L), any further on operation of the DOWN switch does notchange the setting of the change-speed gear position.

When it is determined at step S545 that the DOWN switch is not in the ONposition, that is, in the case where neither the UP switch nor the DOWNswitch is operated, the setting of the change-speed gear position is notchanged. On completion of the setting of the change-speed gear positionat the current gearshift position, the CPU concludes the change-speedgear position setting process and returns to the drive control routine.The change-speed gear position setting process only sets the position ofthe change-speed gear to be used, and the actual changeover of thechange-speed gear position is carried out in the drive control routineas discussed below.

Referring back to the flowchart of FIG. 32, after conclusion of thechange-speed gear position setting process, the CPU executes adeceleration setting process (step S600). This series of the processingsets a target deceleration in response to the operation of the slideknob 161. The details of the deceleration setting process are describedwith FIG. 34.

FIG. 34 is a flowchart showing a routine of the deceleration settingprocess. When the program enters this routine, the CPU first receivessignals from various switches (step S605). The signals input here arethe slide knob signal and the snow mode switch signal among the varioussignals shown in FIG. 7. Other signals may also be input here.

The CPU determines whether or not there is any failure with regard tothe switch of the slide knob 161, in response to the input signal (stepS610). A variety of techniques are applicable to detect the possiblefailure. For example, in the case of a contact failure of the switch,chattering occurs to cause an extremely frequent variation in observedquantity of operation of the slide knob 161. Detection of a variation ofor over a predetermined level leads to detection of the switch failure.The failure of the switch may be detected by any other techniques.

When any failure of the switch is detected, the CPU cancels the currentsetting of the target deceleration (step S615), in order to prevent thedeceleration from being set against the intention of the driver. Theprocessing may alternatively keep the current setting of the targetdeceleration unchanged. The processing adopted in the second embodimenttakes into account the possibility that there is a failure of the switchwhile the driver corrects the deceleration set against the intention ofthe driver, and cancels the current setting of the target deceleration.After the cancellation of the setting of the target deceleration, theCPU gives a failure display, so as to inform the driver of the switchfailure (step S620). A variety of techniques may be applied for thefailure display. The technique adopted in the second embodiment gives asound alarm while flashing the M position indicator. In the case of anyfailure of the switch, the CPU carries out the series of the processingdiscussed above and subsequently exits from the deceleration settingprocess routine.

When it is determined at step S610 that there is no failure of theswitch, the CPU sets the target deceleration according to the quantityof operation of the slide knob 161 (step S625). As discussed previouslywith FIG. 10, the deceleration is set in the range of the straight lineBL to the straight line BU according to the quantity of operation of theslide knob 161. The possible setting range of the deceleration dependsupon the gearshift position. For example, when the current gearshiftposition is the third position (3), the deceleration is set in the rangeallowed at the second speed (2^(nd)) and the third speed (3^(rd)), thatis, in the range of the straight line B3 to the straight line BU shownin FIG. 10. When the current gearshift position is the M position, thedeceleration is set in the range allowed at the position of thechange-speed gear selected by the driver.

After setting the target deceleration, the CPU determines whether or notthe preset target deceleration is within a reject area (step S630). Thisseries of the processing follows the routine of the first embodiment. Inthe case where the target deceleration is within the reject area, theCPU restricts the preset deceleration to an allowable upper limit (stepS635). The CPU then informs the driver of the restriction of the settingof the target deceleration (step S640). The technique adopted in thesecond embodiment flashes the deceleration indicator 224 forapproximately one second, simultaneously with sounding an alarm. When itis determined at step S630 that the preset target deceleration is notwithin the reject area, the processing of steps S635 and S640 isskipped. After setting the target deceleration, the CPU displays theresult of the setting on the deceleration indicator 224 (step S645) andexits from the deceleration setting process routine.

After completion of the deceleration setting process, the programreturns to the drive control routine (FIG. 32). The CPU then determineswhether or not the accelerator pedal is off (step S700), in order tospecify which operation is to be carried out, that is, braking,stationary driving, or acceleration. When the accelerator pedal is off,the CPU executes a change-speed gear position changeover process (stepS710). FIG. 35 is a flowchart showing a routine of the change-speed gearposition changeover process. When the program enters this routine, theCPU first refers to the map (FIG. 31) representing the relationshipbetween the deceleration and the change-speed gear position (step S722).The CPU selects the position of the change-speed gear that attains thetarget deceleration set by the driver, based on this map.

The CPU subsequently determines whether or not there are a plurality ofdifferent positions of the change-speed gear mapped to the targetdeceleration (step S722). As shown in FIG. 31, in the hybrid vehicle ofthe second embodiment, the ranges of the deceleration allowed at therespective change-speed gear positions are partly overlapped. Aplurality of positions of the change-speed gear are accordingly mappedto some target deceleration. The processing of step S722 determineswhether or not the target deceleration is attained at a plurality ofdifferent positions of the change-speed gear.

When it is determined at step S722 that the target deceleration isattained at only one position of the change-speed gear, the CPU sets theposition of the change-speed gear read from the map to the currentposition of the change-speed gear (step S724). When it is determined atstep S722 that the target deceleration is attained at a plurality ofdifferent positions of the change-speed gear, on the other hand, the CPUselects the optimum position of the change-speed gear according to theremaining charge SOC of the battery. In the case where the remainingcharge SOC of the battery is not less than a predetermined value HL, theCPU selects the position of the change-speed gear having a largest gearratio among the plurality of alternatives (step S728). The change-speedgear position having the largest gear ratio means the position of thechange-speed gear closer to the first speed (L).

The change-speed gear position having the larger gear ratio leads to thesmaller braking force to be output from the power source for braking ata fixed deceleration. The larger gear ratio results in the smallerquantity of electric power regenerated by the motor. At somedeceleration, the motor carries out the power operation to relieve thebraking force by the engine 10 and thereby attain the desired brakingcontrol. When the remaining charge SOC of the battery is not less thanthe predetermined value HL, the CPU selects the change-speed gearposition having the least quantity of regenerated electric power, thatis, the change-speed gear position having the largest gear ratio, inorder to prevent the battery from being excessively charged in thebraking process. Any appropriate value is set to the predetermined valueHL used as a criterion of the determination of whether or not the chargelevel of the battery may cause excessive charging. In order to preventthe position of the change-speed gear from being frequently switchedover among the plurality of alternatives according to the remainingcharge of the battery, it is desirable to set a certain hysteresis forthe determination of step S726.

The CPU subsequently restricts the selected change-speed gear positionto a specific range down to one step below the lowest speed allowed atthe current gearshift position (step S730). In the structure of thesecond embodiment, there is no restriction set for the lower limit ofthe change-speed gear position at any gearshift position other than the.M position. Namely any speed down to the first speed (L) is allowed atthe gearshift position other than the M position. No processing is thuspractically carried out at step S730 at the gearshift position otherthan the M position. At the M position, the position of the change-speedgear set by the driver is compared with the position of the change-speedgear selected at step S728. For example, the driver sets the fourthspeed (4^(th)) for the change-speed gear position, while thechange-speed gear position selected at step S728 is either the thirdspeed (3^(rd)) or the fourth speed (4^(th)). In this case, thedifference is only one step, so that no processing is practicallyperformed at step S730. When the change-speed gear position selected atstep S728 is the second speed (2^(nd)), however, the difference from thechange-speed gear position set by the driver is two steps. At step S730,the selected change-speed gear position is accordingly changed to thethird speed (3^(rd)) that is one step below the change-speed gearposition set by the driver.

When it is determined at step S726 that the remaining charge SOC of thebattery is less than the predetermined value HL, the CPU selects theposition of the change-speed gear having a smallest gear ratio (stepS732). In this case, it is required to quickly charge the battery, sothat the desirable selection is the position of the change-speed gearhaving the greatest possible quantity of regeneration. The change-speedgear position having the smaller gear ratio leads to the greaterregenerative loading of the motor to attain a predetermineddeceleration. The CPU accordingly selects the position of thechange-speed gear having the smallest gear ratio, so as to enable thebattery to be charged quickly.

The CPU subsequently restricts the selected change-speed gear positionto a specific range up to one step above the highest speed allowed atthe current gearshift position (step S734). Here the CPU compares theposition of the change-speed gear set by the driver with the position ofthe change-speed gear selected at step S728. For example, when thedriver selects the third (3) position for the current gearshift positionor when the driver sets the third speed (3^(rd)) at the M position, theupper limit of the available change-speed gear position is the thirdspeed (3^(rd)). When the position of the change-speed gear selected atstep S732 is either the third speed (3^(rd)) or the fourth speed(4^(th)), the difference is one step, so that no processing ispractically performed at step S734. When the change-speed gear positionselected at step S732 is the fifth speed (5^(th)), however, thedifference from the upper limit is two steps. At step S734, the selectedchange-speed gear position is accordingly changed to the fourth speed(4^(th)) that is one step above the change-speed gear position set bythe driver.

This corresponds to, for example, the case of attaining the decelerationdefined by a point A shown in the map of FIG. 31. As clearly understoodfrom the map, the deceleration defined by the point A is attained atthree different positions of the change-speed gear, that is, the thirdspeed (3^(rd)) to the fifth speed (5^(th)). When the gearshift positionis the third (3) position, the CPU selects not the fifth speed (5^(th))but the fourth speed (4^(th)) as the position of the change-speed gearattaining the deceleration defined by the point A at step S234.

The change-speed gear position changeover process for the brakingcontrol selects and changes over the position of the change-speed gearacross the range specified by the gearshift position. The technique ofthe second embodiment selects the position of the change-speed gear withpreference to advantageous charging of the battery. When thechange-speed gear position of the transmission 100 is set by the seriesof the processing discussed above, the CPU actually changes over theposition of the change-speed gear (step S750).

On completion of the changeover of the change-speed gear position, theCPU returns to the drive control routine (FIG. 32) and calculates atarget torque to be output from the motor 20 (step S400).

The total torque to be output from the engine 10 and the motor 20functioning as the power source is calculated from the presetdeceleration, that is, the torque to be output to the axle 17, at theselected position of the change-speed gear according to Equations (2)through (6) with the gear ratios k1 through k5. The braking force outputfrom the engine 10, that is, the power of the engine brake, issubstantially unequivocally determined according to the revolving speedof the crankshaft 12. The torque to be output from the motor 20 is thusobtained by subtracting the torque by the engine brake from the totaltorque to be output from the power source.

The change-speed gear position changeover process (FIG. 35) selects theposition of the change-speed gear from the viewpoint of the betterenergy recovery rate, irrespective of the restriction by the gearshiftposition. Such selection, however, does not change the targetdeceleration set by the driver. Namely the position of the change-speedgear should be selected in the range that attains the targetdeceleration. The torque of the motor 20 calculated by the aboveprocessing is accordingly the torque attaining the target decelerationset under the condition of the selected gearshift position.

The procedure of the second embodiment determines the target torque ofthe motor 20 by calculation. Another possible procedure provides a mapto determine the target torque of the motor 20. Still another possibleprocedure measures the deceleration of the vehicle with an accelerationsensor and feedback controls the torque of the motor 20, in order toattain the preset deceleration. Although the calculation of the motortorque is performed after completion of the change-speed gear positionchangeover process in the flowchart of FIG. 32, this is just forconvenience of illustration.

The calculation may thus be performed simultaneously with thechange-speed gear position changeover process.

The CPU then carries out a braking control (step S905) based on thetarget torque determined as discussed above, so as to control operationsof the motor 20 and the engine 10. The CPU stops the fuel injection tothe engine 10 and the ignition, in order to apply the engine brake. TheCPU may simultaneously control the VVT mechanism incorporated in theengine 10. Since the deceleration by the power-source braking can beregulated by the torque of the motor 20, the procedure of the secondembodiment does not control the VVT mechanism here.

The motor 20 is driven by the PWM control. The CPU sets a voltage to beapplied to the coils on the stator 24 in the motor 20. The voltage isdetermined corresponding to the revolving speed and the target torque ofthe motor 20, based on a preset table. In the case of the regenerativeoperation of the motor 20, a negative value is set to the voltage. Inthe case of the power operation of the motor 20, on the contrary, apositive value is set to the voltage. The CPU controls the on-offconditions of the respective transistors included in the driving circuit40, in order to cause the preset voltage to be applied to the coils. ThePWM control is a known technique and is thus not described in detailhere.

When it is determined at step S700 that the accelerator pedal is notoff, that is, the accelerator pedal is stepped on, the CPU carries out acontrol process for the stationary driving or acceleration.

For the purpose of the control, the CPU changes over the position of thechange-speed gear (step S910). The changeover of the change-speed gearposition in the course of the stationary driving or acceleration followsthe map of the first embodiment shown in FIG. 10. The processing of stepS910 carries out the change to the position of the change-speed gear setby the change-speed gear position setting process (FIG. 33). Theposition of the change-speed gear in the course of the stationarydriving or acceleration is changed over in the range specified by thegearshift position set by the driver.

After setting the position of the change-speed gear, the CPU sets thedriving points of the engine 10 and the motor 20 (step S915). Asdescribed previously, the hybrid vehicle of the second embodiment hastwo drive modes selectively used according to the vehicle speed and thetorque, that is, the motor drive mode using only the motor 20 as thepower source and the engine drive mode using only the engine 10 as thepower source. There is no drive mode using both the motor 20 and theengine 10 as the power source. The CPU selects the appropriate drivemode according to the driving state of the vehicle and sets the drivingpoints of the engine 10 and the motor 20 that can output the powercorresponding to the step-on amount of the accelerator pedal. Aftersetting the respective driving points, the CPU carries out a cruisingand acceleration control (step S920), so as to control operations of theengine 10 and the motor 20. The concrete procedures of the control areidentical with those carried out at step S905.

The hybrid vehicle of the second embodiment repeatedly carries out thedrive control routine discussed above, so as to implement the brakingcontrol by the power source braking. The hybrid vehicle may also carryout the braking control by the wheel braking in combination with thebraking control by the power source braking. The following describes oneexemplified process of changing over the change-speed gear positionunder the condition of the varying deceleration in the hybrid vehicle ofthe second embodiment. FIG. 36 shows the relationship between thesetting of the deceleration and the changeover of the change-speed gearposition as an example. In the example of FIG. 36, the fourth (4)position is selected as the current gear shift position.

The driver operates the slide knob 161 to lower the deceleration in atime period e1 to e3. The slide knob 161 is slid from the front to theback. The target deceleration of the vehicle continuously decreases inresponse to this operation as shown in FIG. 36.

It is here assumed that the initial deceleration is attained at thesecond speed (2^(nd)) only by the engine brake. When the targetdeceleration decreases in a time period e1, the change-speed gearposition is changed over to the third speed (3^(rd)) that is the upperspeed by one step. The motor 20 then carries out the regenerativeoperation for braking. In order to lower the deceleration at the secondspeed (2^(nd)), the motor 20 is required to carry out the poweroperation. The power operation is, however, disadvantageous from theviewpoint of the energy recovery rate. This is why the change-speed gearposition is changed over to the third speed (3^(rd)). In the time periode1, the quantity of regeneration by the motor 20 is reduced to attainthe deceleration in response to the operation of the slide knob 161.

In a time period e2 after the quantity of regeneration by the motor 20reaches the value ‘0’ at the third speed (3^(rd)), with a view toenhancing the energy recovery rate, the change-speed gear position isfurther changed over to the fourth speed (4^(th)) that is the upperspeed by another one step. The motor 20 again carries out theregenerative operation for braking. In the time period e2, the quantityof regeneration by the motor 20 is reduced to attain the deceleration inresponse to the operation of the slide knob 161.

Similarly, in a time period e3 after the quantity of regeneration by themotor 20 reaches the value ‘0’ at the fourth speed (4^(th)), with a viewto enhancing the energy recovery rate, the change-speed gear position isfurther changed over to the fifth speed (5^(th)) that is the upper speedby still another one step. The motor 20 again carries out theregenerative operation for braking. When the fourth (4) position isselected as the current gearshift position, the upper limit of thechange-speed gear position is originally restricted to the fourth speed(4^(th)). Under such restriction, as shown by the one-dot chain line inFIG. 36, the motor 20 carries out the power operation for braking at thefourth speed (4^(th)). This undesirably lowers the energy recovery rate.In the hybrid vehicle of the second embodiment, the position of thechange-speed gear is selectable in the course of braking, irrespectiveof the restriction by the gearshift position. The braking control at thefifth speed (5^(th)) is accordingly carried out in the time period e3.

The hybrid vehicle of the second embodiment discussed above selects thechange-speed gear position that is advantageous from the viewpoint ofthe energy recovery rate in the course of braking, irrespective of therestriction by the gearshift position. This arrangement enhances theenergy recovery rate of the vehicle in the braking process. The brakingcontrol is naturally carried out with the deceleration set under thecondition of the selected gearshift position. The driver accordinglyutilizes the power source braking without feeling any incompatibility.

During the stationary driving or acceleration, on the other hand, theposition of the change-speed gear is set according to the gearshiftposition. For example, it is assumed that the fifth speed (5^(th)) isactually used in the braking process at the fourth (4) position.

When the driver steps on the accelerator pedal after the brakingcontrol, the position of the change-speed gear is immediately changedover to the fourth speed (4^(th)) for further driving. This arrangementensures the quick acceleration required by the driver, subsequent to thebraking control.

The hybrid vehicle of the second embodiment enhances the energy recoveryrate in the braking process, while actualizing the speed reduction andacceleration meeting the requirements of the driver. This arrangementenhances the effectiveness of the power source braking and improves thecontrollability of the vehicle.

The second embodiment regards the case of selecting the change-speedgear position suitable for charging the battery as one exemplifiedprocess of selecting the change-speed gear position with preference tothe energy recovery rate. The selection of the change-speed gearposition may, however, be carried out from another point of view. Onemodified procedure selects the position of the change-speed gear givingthe highest regenerative energy.

The hybrid vehicle of the second embodiment selects the position of thechange-speed gear in the specific range that allows deviation by onestep respectively from the upper limit and the lower limit specified bythe gearshift position. This arrangement facilitates the control of thetransmission in a transient period from braking to another driving statein the hybrid vehicle of the second embodiment. In the case where thebraking control is carried out with the change-speed gear position thatdeviates from the specified change-speed gear position by several steps,it is necessary to change the change-speed gear position over theseveral steps in the transient period from the braking control to thestationary driving or acceleration. The control actualizing such achange is undesirably complicated, and the changeover of thechange-speed gear position requires a relatively long time. This mayinterfere with the quick acceleration subsequent to braking. The hybridvehicle of the second embodiment selects the position of thechange-speed gear in the specific range that allows deviation only byone step respectively from the upper limit and the lower limit specifiedby the gearshift position. This arrangement thus effectively preventsthe possible troubles discussed above.

B3. First Modification of Second Embodiment

In the case where the changeover of the change-speed gear position byseveral steps subsequent to braking is permitted from both theviewpoints of the control procedure to perform the changeover and thetime period required for the changeover, the selection of thechange-speed gear position is allowed in the range that deviates by twoor more steps from the restricted region by the gearshift position. Aconcrete example of the change-speed gear position changeover process insuch cases is described with FIG. 37.

FIG. 37 is a flowchart showing a routine of the change-speed gearposition changeover process as a modified example. This replaces theprocessing of steps S722 through S734 in the flowchart of FIG. 35. Thehybrid vehicle of the second embodiment has at most three positions ofthe change-speed gear mapped to one deceleration as shown in the map ofFIG. 10. The processing of FIG. 37 selectively uses one of the threepositions of the change-speed gear with preference to the energyrecovery rate.

After the selection of the change-speed gear position attaining thetarget deceleration, the CPU determines whether or not there is only onechange-speed gear position mapped to the target deceleration (stepS722′). When the target deceleration is attained at only one position ofthe change-speed gear, the CPU sets the position of the change-speedgear read from the map to the current position of the change-speed gear(step S724′).

When it is determined at step S722 that the target deceleration isattained at a plurality of different positions of the change-speed gear,on the other hand, the CPU subsequently determines whether the targetdeceleration is attained at two different change-speed gear positions ormore (step S725). When it is determined that there are two differentpositions of the change-speed gear mapped to the target deceleration,the CPU refers to the remaining charge SOC of the battery 50 andcompares the remaining charge SOC with a predetermined value HL (stepS726). In the case where the remaining charge SOC is not less than thepredetermined value HL, the CPU selects the position of the change-speedgear having the lesser quantity of regenerated electric power, that is,the position of the change-speed gear having a larger gear ratio out ofthe two alternatives (step S728), with a view to preventing the battery50 from being excessively charged. In the case where the remainingcharge SOC is less than the predetermined value HL, on the other hand,the CPU selects the position of the change-speed gear suitable forcharging the battery 50, that is, the position of the change-speed gearhaving a smaller gear ratio out of the two alternatives (step S732).

When it is determined that there are more than two different positionsof the change-speed gear, that is, there are three different positionsof the change-speed gear, mapped to the preset deceleration, the CPUcompares the remaining charge SOC of the battery 50 with twopredetermined threshold values H1 and H2 (step S736). A relationshipH1<H2 holds between these threshold values. In the case where theremaining charge SOC is not less than the threshold value H2, the CPUselects the position of the change-speed gear most suitable forcharging, that is, the position of the change-speed gear having alargest gear ratio (step S737). In the case where the remaining chargeSOC is less than the threshold value H2 but is not less than thethreshold value H1, the CPU selects the position of the change-speedgear having an intermediate gear ratio out of the three alternatives(step S738). In the case where the remaining charge SOC is less than thethreshold value H1, the CPU selects the position of the change-speedgear having the least quantity of regenerated electric power, that is,the position of the change-speed gear having a smallest gear ratio (stepS739).

The threshold values H1 and H2 used for the decision at step S736 arecriteria to change over the position of the change-speed gear.

Appropriate values are set to the threshold values H1 and H2, so thatthe optimum position of the change-speed gear having the desiredquantity of regenerated electric power is selected corresponding to thecharge level of the battery 50. Both the threshold values H1 and H2 maybe different from the reference value HL used at step S726, oralternatively either one of the threshold value H1 and H2 may becoincident with the reference value HL. In the change-speed gearposition selection routine of the modified example, it is also desirableto set certain hystereses for the decisions of steps S726 and S736, inorder to prevent the position of the change-speed gear from beingfrequently switched over between and among the alternatives according tothe remaining charge SOC.

Selection among the three or more positions of the change-speed gearadvantageously enables the charge level of the battery to be regulatedminutely. The above example shows the processing to selectively use thethree change-speed gear positions. The similar processing may, however,be applicable to the arrangement of performing the selection among agreater number of change-speed gear positions.

It is desirable to restrict the selectable range of the change-speedgear position, so that the difference between the gear ratio regionspecified by the gearshift position and the gear ratio actually used inthe braking control is within a predetermined range. As describedpreviously, the technique of the second embodiment changes over theposition of the change-speed gear according to the gearshift position,after the braking control. In the case where there is a large differencebetween the gear ratio used in the braking process and the gear ratioused after the braking control, the driving conditions of the engine 10and the motor 20 significantly vary with the changeover of thechange-speed gear position after the braking control. If the variationis extremely large, some troubles may arise; for example, a significantvibration occurs in the vehicle or the driving state of the engine 10becomes unstable. The restriction to make the difference between thegear ratio region specified by the gearshift position and the gear ratioactually used in the braking control within the predetermined range thatdoes not cause such a large variation ensures the speed reduction andacceleration without any of the above troubles, and thereby attains thesmooth driving. The predetermined range of the gear ratio may be set byexperiments or analyses, based on the response to the control of theengine 10 and the speed of the changeover of the change-speed gearposition.

B4. Second Modification of Second Embodiment

The relationship between the gearshift position and the deceleration isnot restricted to the settings described in the second embodiment. FIG.38 shows the settings of the deceleration as a second modified example.The deceleration may be changed only with regard to the change-speedgear position having the smallest gear ratio among all the change-speedgear positions used at each gearshift position. The map of FIG. 38 showsan example of the settings at the D position. The available change-speedgear position at the D position ranges from the first speed (L) to thefifth speed (5^(th)). The change-speed gear position having the smallestgear ratio is the fifth speed (5^(th)). In response to an operation ofthe slide knob 161 at the D position, the deceleration corresponding tothe fifth speed (5^(th)) is changed in the range shown in FIG. 38. Thedeceleration is unchanged and kept at the preset values, however, at thechange-speed gear positions of and below the fourth speed (4^(th)),irrespective of the operation of the slide knob 161. The map of FIG. 38shows the resulting settings of the deceleration at the respectivepositions of the change-speed gear. The deceleration at the first speed(L) is omitted from the illustration, since it is too high.

In the case of such settings of the deceleration, the series of thecontrol processing executed in the second embodiment and shown in FIGS.32 through 35 are adopted to carry out the speed reduction control. Inthis case, the processing of steps S410 through S420 may be omitted fromthe drive control process of the second embodiment (FIG. 32).

As clearly understood from FIG. 38, the deceleration set in response tothe operation of the slide knob 161 corresponds to the lower limit ofthe power source braking applied to the vehicle. At the D position, thedeceleration is changed during a drive at the fifth speed (5^(th)) inresponse to the operation of the slide knob 161.

During a drive at the fourth speed (4^(th)), however, the minimumdeceleration required by the driver has been assured, so that thebraking control is carried out with the preset deceleration. In the casewhere the M position is selected to enable the driver to manually changeover the position of the change-speed gear, only the deceleration at thechange-speed gear position selected by the driver is changed in responseto the slide knob 161.

B5. Third Modification of Second Embodiment

FIG. 39 shows the settings of the deceleration as a third modifiedexample. The map of FIG. 39 shows an example of the settings at thethird (3) position. The available change-speed gear position at theposition 3 ranges from the first speed (L) to the third speed (3^(rd)).The change-speed gear position having the smallest gear ratio is thethird speed (3^(rd)). In response to an operation of the slide knob 161at the position 3, the deceleration corresponding to the third speed(3^(rd)) is changed in the range sown in FIG. 39. The deceleration isunchanged and kept at the preset values, however, at the change-speedgear positions of and below the second speed (2^(nd)), irrespective ofthe operation of the slide knob 161. At the position 3, the fourth speed(4^(th)) and the fifth speed (5^(th)) are not used, and the decelerationis thus not changed at these change-speed gear positions.

In the case of such settings of the deceleration, the series of thecontrol processing executed in the second embodiment and shown in FIGS.32 through 35 are adopted to carry out the speed reduction control. Inthis case, the processing of steps S410 through S420 may be omitted fromthe drive control process of the second 20 embodiment (FIG. 32). Likethe second modified example, the settings of the third modified exampleassure the minimum deceleration required by the driver and accordinglyenables the braking control to be carried out with the presetdeceleration.

B6. Fourth Modification of Second Embodiment

FIG. 40 shows the settings of the deceleration using the slide knob 161in a fourth modified example. FIG. 41 shows the settings of thedeceleration by operating the slide knob 161 in an increasing direction.Straight lines 2^(nd) through 5^(th) in FIG. 41 respectively show theresulting settings of the deceleration. Straight lines b2 through b5 inFIG. 41 correspond to straight lines 2^(nd) to 5^(th) in FIG. 40.

In this modified example, the deceleration is changed not only at thechange-speed gear position having the smallest gear ratio but at all thechange-speed gear positions, in response to the operation of the slideknob 161. The braking control is accordingly carried out with the higherdecelerations than the settings of FIG. 40 against any vehicle speed.This arrangement enables the deceleration to be changed in any caseincluding a drive with the smallest gear ratio, thus attaining thebraking control satisfying the driver's feeling.

In still another modification, the settings of the deceleration may bechanged between the M position and the other gearshift positions. Inthis modification, the map of FIG. 40 shows the settings of thedeceleration at the D position, whereas the map of FIG. 41 shows thesettings of the deceleration when the M position is selected without theoperation of the slide knob 161. In this manner, the deceleration at theM position may be set higher than the deceleration at the D positionover all the speed-change gear positions.

Under the selection of the M position, the high controllability isgenerally required. The higher deceleration at the M position than thedeceleration at the D position is often required for the brakingcontrol. The arrangement of setting the deceleration at the M positionhigher than the deceleration at the D position does not require thesettings of the deceleration to be changed again in response to theselection of the M position but attains the braking control satisfyingthe driver's feeling.

Any combination of the above arrangements may be applied for thevariation in deceleration at each gearshift position in response to theoperation of the slide knob 161. One applicable process varies only thedeceleration at the fifth speed (5^(th)) when the current gearshiftposition, is at the D position. The process varies the deceleration atall the change-speed gear positions when the current gearshift positionis at the fourth (4) position. As described above, any arrangement maybe applied for the settings of the deceleration as long as it issuitable for implementing the braking control satisfying the driver'sfeeling.

C. Third Embodiment

The following describes a third embodiment according to the presentinvention. FIG. 42 schematically illustrates the structure of a hybridvehicle in the third embodiment. The difference from the firstembodiment is that the hybrid vehicle of the third embodiment has adifferent power transmission pathway from the power source to the axle17. In the hybrid vehicle of the third embodiment, the engine 10, thetorque converter 30, the transmission 100, and the motor 20 areconnected in this sequence. The output shaft 15 of the motor 20 islinked with;the axle 17 via the differential gear 16. A clutch 170 isinterposed between the engine 10 and the torque converter 30. The clutch170 works by means of oil pressure to connect and disconnect the powertransmission between the engine and the torque converter 30. Theoperations of the clutch 170 are controlled by the control unit 70. Thedetailed structures of the respective constituents including the torqueconverter 30, the transmission 100, and the motor 20 are identical withthose in the first embodiment.

In the structure of the third embodiment, the driver operates the Decelswitch and the Can-Decel switch to regulate the deceleration. Theoperation of the SNOW switch 163 restricts the upper limit of thepossible range of setting of the deceleration.

FIG. 43 is a flowchart showing a speed reduction control routineexecuted in the third embodiment. Like the first embodiment, the CPU inthe control unit 70 executes this series of the processing. When theprogram enters this routine, the CPU first carries out the initialsetting process and the deceleration setting process (steps S10 andS100). These processes are practically the same as the processesdiscussed in the first embodiment (FIGS. 16 through 18).

The initial setting.process specifies the initial setting of thedeceleration and cancels the setting according to the gearshiftposition. In the first embodiment, the initial setting process sets theinitial value to the position of the change-speed gear (step S50 in FIG.16). The third embodiment, however, does not require the control of thechange-speed gear position in the process of E position braking asdescribed later and thus omits the step of setting the initial value tothe position of the change-speed gear.

Like the first embodiment, the deceleration setting process sets thetarget deceleration in response to the operations of the Decel switchand the Can-Decel switch. The deceleration restricting process is alsocarried out to restrict the upper limit of the targetdeceleration,:based on the selection or non-selection of the snow mode.The technique of the third embodiment executes these series of theprocessing to set the adequate target deceleration according to thedriving state of the hybrid vehicle. The technique of the firstembodiment uses the table (FIG. 11) that enables the target decelerationto be set in a wide range accompanied with the changeover of thechange-speed gear position. In the structure of the third embodiment, onthe other hand, the gear ratio does not have any effects on the brakingforce under the E position braking control, so that the targetdeceleration is set in a specific range attained by only the motor 20.

The CPU subsequently determines whether or not the braking control bythe power source braking is to be carried out, based on the input signalregarding the accelerator travel (step S200). The CPU then determineswhether or not the E position braking control is allowed, based on thesame criteria as those of the first embodiment (step S205). In the casewhere the E position braking control is not allowed, the CPU sets apredetermined value Tm0 to the target torque of the motor and carriesout a standard braking control (steps S210 and S250). These processesare identical with those executed in the first embodiment and are thusnot specifically described here.

In the case where the E position braking control is allowed, on theother hand, a certain control process for the E position brakingcontrol, which is different from that of the first embodiment, iscarried out. In the E position braking control process, the CPU firstreleases the clutch (step S844). The concrete procedure regulates theoil pressure in the clutch 170 to disconnect the power transmissionbetween the engine 10 and the torque converter 30.

The CPU subsequently calculates the target torque of the motor 20 (stepS845). The technique of the first embodiment calculates the targettorque of the motor from the gear ratio according to the position of thechange-speed gear. In the structure of the third embodiment, the motor20 is connected with the output shaft 15 not via the transmission 100but directly as shown in FIG. 42. Release of the clutch 170 causes theengine not to contribute to the braking control. Under such conditions,only the motor 20 applies the braking force for the power sourcebraking. In the structure of the third embodiment, the target torque ofthe motor 20 is thus determined unequivocally according to the currentlyset target deceleration. In the case where the target deceleration isset using the braking torque of the output shaft 15 as a parameter, thebraking torque is set to the target torque of the motor 20. The targettorque may be calculated from the target deceleration according topreset arithmetic operations or may alternatively be read from a presettable.

After setting the target torque, the CPU carries out the E positionbraking control (step S851). In the structure of the third embodiment,the driving state of the engine does not contribute to the brakingcontrol, so that no special control is carried out for the operations ofthe engine. The CPU simply drives the engine at idle or stops theengine. No special control is also carried out for the transmission 100since the transmission 100 does not affect the braking control. The CPUkeeps the previous gear ratio without any change. The motor 20 performsthe regenerative operation with the preset target torque. The controlprocedure of the motor follows the description of the first embodiment.

The hybrid vehicle of the third embodiment carries out the series of theprocessing discussed above, so as to implement the braking control bythe power source braking with the deceleration set by the driver. In thecase where the snow mode is set, for example, under the condition of thelow friction coefficient of the road surface, the upper limit of thedeceleration is restricted to ensure the braking control by the powersource braking in a stable driving range.

The hybrid vehicle of the third embodiment has additional advantages.The first additional advantage is that the hybrid vehicle of the thirdembodiment facilitates the braking control. In the structure of thethird embodiment, the clutch 170 is released in the process of Eposition braking, so that neither the transmission 100 nor the engine 10contributes to the braking control. An unequivocal relationshipaccordingly holds between the target deceleration and the target torqueof the motor 20. This significantly facilitates the process of settingthe target torque of the motor 20. This arrangement does not require thechange of the gear ratio with a variation in vehicle speed in the courseof braking. These facts significantly simplifies the braking controlprocess in the third embodiment.

The second additional advantage is that the hybrid vehicle of the thirdembodiment has improved energy efficiency. In the structure of the thirdembodiment, the clutch 170 is released to prevent the kinetic energy ofthe hybrid vehicle from being consumed in the form of heat by enginebrake. The hybrid vehicle of the third embodiment thus reduces apossible energy loss in the process of regenerating the kinetic energyof the vehicle by means of the motor 20.

The third additional advantage is that the hybrid vehicle of the thirdembodiment carries out the more efficient and appropriate control in thesnow mode. In the hybrid vehicle of the first embodiment, the drivingforce is applied by the engine brake even when the target torque of themotor 30 is equal to zero. The motor 30 should carry out the poweroperation, in order to give the braking force of less than the enginebrake. In the hybrid vehicle of the third embodiment, on the other hand,the engine 10 does not contribute to the braking control. Regulating thetarget torque of the motor 30 thus enables the power source braking withthe smaller braking force than that by the engine brake to be actualizedby regenerative braking. There is no need to take into account thebalance with the engine brake. This ensures the stable application ofthe target braking force. Even under the condition of the extremelysmall friction coefficient of the road surface, this arrangement ensuresthe efficient and stable braking control of the hybrid vehicle.

A variety of modifications are applicable to the hybrid vehicle of thethird embodiment. The third embodiment regards the case of releasing theclutch 170 every time the E position braking control is performed. Onemodified procedure controls the release of the clutch 170 according tothe driving state of the hybrid vehicle. For example, when the battery50 has the remaining charge close to the full charge level, which doesnot allow the sufficient regenerative braking, the E position controlprocess is carried out with the clutch 170 kept in a coupled position.This arrangement ensures the appropriate braking control by the powersource braking irrespective of the charge level of the battery 50, thusimproving the facility of the power source braking and enhancing thecontrollability of the hybrid vehicle. The release and the coupling ofthe clutch 170 may be controlled according to a diversity of otherconditions.

A variety of modifications are also applicable to the hardwareconfiguration. In the description below, the side of the engine 10 isdefined as the upstream side and the side of the axle 17 is defined asthe downstream side in the pathway of power transmission from the engine10 to the axle 17. In the hybrid vehicle shown in FIG. 25, the clutch170 is interposed between the engine 10 and the torque converter 30. Theclutch 170 may, however, be disposed at any position upstream the motor20.

Like the first embodiment, the technique of the third embodiment isapplicable to the series hybrid vehicle. In this case, the hybridvehicle may have the structure of FIG. 29 without the torque converter30A and the transmission 100A. The vehicle may be constructed by furtheromitting the engine 10A and the generator G.

In accordance with another modified structure, the engine 10, the motor20, the torque converter 30, and the transmission 100 are connected inthis sequence from the upstream side like the first embodiment, and theclutch 170 is interposed between the engine 10 and the motor 20. In thismodified structure, the change-speed gear position selection process(see FIG. 23) is carried out in the course of E position braking controlas discussed in the first embodiment. This arrangement enables thebraking control to be carried out by the motor in a wide range whileeffectively utilizing the advantage that the engine does not contributeto the braking control.

D. Fourth Embodiment

The above embodiments regard the hybrid vehicle having the engine andthe motor as the available energy output source for driving. Thetechnique of the present invention is applicable to a variety ofvehicles having the structure that enables regenerative braking by themotor. For example, the principle of the present invention may beapplied to a vehicle that uses a motor mainly to drive auxiliarymachinery while the engine is at a stop, to start the engine, and tocarry out the regenerative braking, and does not use the motor, inprinciple, as the power source for driving. An example of suchapplication is described below as a fourth embodiment of the presentinvention.

FIG. 44 schematically illustrates the structure of a vehicle in thefourth embodiment. This vehicle has an engine 310 as the power sourcefor driving. The power of the engine 310 is transmitted for driving inthe sequence of a torque converter 330, a transmission 335, the driveshaft 15, the differential gear 16, and the axle 17. The structures ofthe torque converter 330 and the transmission 335 are identical withthose of the torque converter 30 and the transmission 100 in the firstembodiment.

In the vehicle of the fourth embodiment, a pulley 316 is connected witha crankshaft of the engine 310 via a clutch 314. The pulley 316 isfurther connected with auxiliary machinery 312 and a motor 320 via apower transmission belt 318 that allows mutual power transmission. Theauxiliary machinery 312 includes a compressor of an air conditioner andan oil pump for power steering. The motor 320 is a synchronous motor andis driven with a battery 350 as the electric supply through switchingoperations of an inverter 340 working as a driving circuit. The motor320 is rotated by an external force to function as a generator.

The operations of the respective constituents included in the vehicle ofthe four embodiment are controlled by a control unit 370. Although notbeing illustrated, signals from various switches and sensors that enablethe driver to specify the speed reduction rate are input into thecontrol unit 370 in the same manner as discussed in the firstembodiment.

The following describes general operations of the vehicle of the fourthembodiment. As mentioned previously, the vehicle is driven with thepower of the engine 310. During the drive, the clutch 314 is coupled, soas to cause the auxiliary machinery 312 to be driven with the power ofthe engine 310.

While the clutch 314 is coupled, the motor 320 is rotated via the powertransmission belt 318, so that the vehicle is braked by the regenerativeoperation of the motor 320.

When the vehicle stops even temporarily, for example, at a trafficlight, the control unit 370 stops the operation of the engine 310. Atthe same time, the control unit 370 releases the clutch 314, so as tocause the motor 320 to carry out the power operation and drive theauxiliary machinery 312 with the power of the motor 320. In order tostart driving the vehicle, which has been at a stop, the control unit370 couples the clutch 314 to crank the engine 310 with the power of themotor 320 and start the engine 310. During the drive, the power of themotor 320 is used, in principle, only for cranking the engine 310. Onepossible modification continues the operation of the motor 320 to assistthe power at the time of starting the vehicle, until the vehicle reachesa preset vehicle speed.

The vehicle of the fourth embodiment stops the operation of the engine310 while the vehicle is at a stop. This arrangement effectively savesthe fuel consumption.

The vehicle of the fourth embodiment enables the regenerative braking bythe motor 320 and thus readily attains the speed reduction correspondingto the step-on amount of the accelerator pedal like the firstembodiment. The connection of the motor 320, the engine 310, the torqueconverter 330, and the transmission 335 under the coupling condition ofthe clutch 314 is equivalent to the connection in the first embodiment,from the viewpoint of the application of the braking force. The seriesof the control processing discussed in the first embodiment isaccordingly applied for the braking control executed in the vehicle ofthe fourth embodiment. The torque by the regenerative braking of themotor 320 is transmitted to the drive shaft 15 via the transmission 335.Like the first embodiment, the total control of the transmission 335 andthe torque of the motor 320 enables the speed reduction rate to becontrolled in a wide range.

As described above, the present invention is not restricted to thevehicle with the motor mounted thereon for driving. The fourthembodiment regards the structure in which the braking torque of themotor 320 is transmitted to the drive shaft 15 via the transmission 335.The vehicle may, however, have a motor for regenerative braking that isdirectly connected with the drive shaft 15.

E. Other Modifications

In the embodiments discussed above, the driver specifies the targetdeceleration. The speed reduction rate is, however, not restricted tothe deceleration, but a braking force or a braking rate applied to thewheels may be set to the speed reduction rate. The above embodimentsregard the process of controlling the regenerative braking by means ofthe motor with the target torque as the parameter. A variety of otherbraking force-related parameters may, however, be used in place of thetorque. For example, the electric power generated by the regenerativebraking or the electric current flowing through the motor may be used asthe parameter of the control.

The embodiments described above respectively use the transmission 100that changes the gear ratio in a stepwise manner. Any other suitablestructure, for example, a mechanism of continuously varying the gearratio, may be employed for the transmission 100.

The present invention is not restricted to the above embodiments ortheir modifications, but there may be many other modifications, changes,and alterations without departing from the scope or spirit of the maincharacteristics of the present invention. In one possible modification,the variety of control procedures discussed in the above embodiments maybe actualized by the hardware configuration. Another modificationcarries out only part of the variety of control procedures discussed inthe above embodiments.

Industrial Applicability

The technique of the present invention is preferably applied to avehicle that may be braked with a motor as well as with a mechanicalbrake utilizing a frictional force, and also to a method of controllingsuch a vehicle.

What is claimed is:
 1. A vehicle comprising a motor, a transmission thatenables selection of a plurality of gear ratios in a process of powertransmission, and a drive shaft, which are connected with one another,said vehicle being braked by means of a torque output from said motor,said vehicle comprising: an operation unit, through an operation ofwhich a driver of said vehicle specifies a speed reduction rate in aprocess of braking with said motor; a target speed reduction ratesetting unit that sets a target speed reduction rate in response to theoperation of said operation unit; a selection unit that selects a targetgear ratio among a plurality of available gear ratios, the target gearratio enabling the currently set target speed reduction rate to beattained by the torque of said motor; a motor driving statespecification unit that specifies a target driving state of said motor,in order to enable a braking force that attains the currently set targetspeed reduction rate to be applied to said drive shaft; and a controlunit that controls said transmission to attain the target gear ratio anddrives said motor in the specified target driving state.
 2. A vehicle inaccordance with claim 1, said vehicle further comprising an engine in aspecific state of linkage that enables a braking torque to be applied tosaid drive shaft, wherein said selection unit selects the target gearratio, based on the torques of said motor and said engine, and saidmotor driving state specification unit sets a target torque of saidmotor by taking into account the braking torque applied by said engine.3. A vehicle in accordance with claim 1, said vehicle furthercomprising: a storage unit, in which a relationship between the targetspeed reduction rate and the target gear ratio is stored, wherein saidselection unit selects the target gear ratio by referring to saidstorage unit.
 4. A vehicle in accordance with claim 1, said vehiclefurther comprising: a changeover unit that changes over a selectablegear ratio range for the target gear ratio in response to apredetermined operation by said driver of said vehicle, wherein saidoperation unit has a mechanism that ensures the specification of thespeed reduction rate in response to another operation of said changeoverunit that is different from the predetermined operation for thechangeover.
 5. A vehicle in accordance with claim 1, wherein said targetspeed reduction rate setting unit comprises: a detection unit thatmeasures a number of times of operation of said operation unit; and aunit that sets the target speed reduction rate in a stepwise manneraccording to the observed number of times of operation.
 6. A vehicle inaccordance with claim 1, wherein said target speed reduction settingunit comprises: a detection unit that measures an operation time of saidoperation unit; and a unit that sets the target speed reduction rateaccording to the observed operation time.
 7. A vehicle in accordancewith claim 1, wherein said target speed reduction setting unitcomprises: a detection unit that measures a quantity of operation ofsaid operation unit; and a unit that sets the target speed reductionrate according to the observed quantity of operation.
 8. A vehicle inaccordance with claim 1, said vehicle further comprising: a switch thatgives an instruction to execute braking with the specified speedreduction rate in response to a predetermined operation by said driverof said vehicle; and a permission unit that allows operations of allsaid target speed reduction rate setting unit, said selection unit, saidmotor driving state specification unit, and said control unit only inthe case where the braking execution instruction is given by means ofsaid switch.
 9. A vehicle in accordance with claim 8, said vehiclefurther comprising: a changeover unit that changes over a selectablegear ratio range for the target gear ratio in response to apredetermined operation by said driver of said vehicle, wherein saidswitch has a mechanism that gives the braking execution instruction inresponse to another operation of said changeover unit that is differentfrom the predetermined operation for the changeover.
 10. A vehicle inaccordance with claim 8, said vehicle further comprising: an informationunit that informs said driver of a result of the instruction whether ornot to execute the braking with the specified speed reduction rate. 11.A vehicle in accordance with claim 1, wherein said target speedreduction rate setting unit comprises: a decision unit that determineswhether the operation of said operation unit is valid or invalid; and aprohibition unit that prohibits the setting of the target speedreduction rate from being changed when it is determined that theoperation is invalid.
 12. A vehicle in accordance with claim 11, whereinsaid operation unit has a mechanism that allows said driver to give aninstruction to increase the speed reduction rate simultaneously with aninstruction to decrease the speed reduction rate, and said decision unitdetermines that the operation of said operation unit is invalid in thecase where the increase instruction is given simultaneously with thedecrease instruction.
 13. A vehicle in accordance with claim 1, whereinsaid operation unit has a mechanism that gives an instruction to varythe speed reduction rate, and said target speed reduction rate settingunit varies the speed reduction rate relative to a preset initial speedreduction rate as a standard level, in response to the operation of saidoperation unit, thereby setting the target speed reduction rate.
 14. Avehicle in accordance with claim 13, said vehicle further comprising: aswitch that gives an instruction to execute braking with the specifiedspeed reduction rate in response to a predetermined operation by saiddriver of said vehicle; a permission unit that allows operations of allsaid target speed reduction rate setting unit, said selection unit, saidmotor driving state specification unit, and said control unit in thecase where the braking execution instruction is given; and an ordinarybraking unit that carries out braking with a predetermined speedreduction rate, irrespective of the operation of said operation unit, inthe case where the braking execution instruction is not given, whereinthe initial speed reduction rate is set equal to the predetermined speedreduction rate employed by said ordinary braking unit.
 15. A vehicle inaccordance with claim 11, said vehicle further comprising: a switch thatgives an instruction to execute braking with the specified speedreduction rate in response to a predetermined operation by said driverof said vehicle; a permission unit that allows operations of all saidtarget speed reduction rate setting unit, said selection unit, saidmotor driving state specification unit, and said control unit in thecase where the braking execution instruction is given; and an ordinarybraking unit that carries out braking with a predetermined speedreduction rate, irrespective of the operation of said operation unit, inthe case where the braking execution instruction is not given, whereinthe initial speed reduction rate is set to be significantly greater thanthe predetermined speed reduction rate employed by said ordinary brakingunit.
 16. A vehicle in accordance with claim 11, wherein said targetspeed reduction rate setting unit comprises: a cancellation decisionunit that determines whether or not the target speed reduction rate isto be cancelled; and a setting cancellation unit that resets the targetspeed reduction rate to the initial speed reduction rate when it isdetermined that the target speed reduction rate is to be cancelled. 17.A vehicle in accordance with claim 16, said vehicle further comprising:a switch that gives an instruction to execute braking with the specifiedspeed reduction rate in response to a predetermined operation by saiddriver of said vehicle, wherein said cancellation decision unitdetermines that the target speed reduction rate is to be cancelled inresponse to an operation of said switch.
 18. A vehicle in accordancewith claim 15, said vehicle further comprising: a failure detection unitthat detects a failure of said operation unit, wherein said cancellationdecision unit determines that the target speed reduction rate is to becancelled in response to detection of the failure.
 19. A vehicle inaccordance with claim 1, wherein said selection unit selects the targetgear ratio with preference to a preset initial value.
 20. A vehicle inaccordance with claim 19, said vehicle further comprising: a switch thatgives an instruction to execute braking with the specified speedreduction rate in response to a predetermined operation by said driverof said vehicle, wherein the preset initial value is equal to a previousgear ratio immediately before the braking execution instruction is givenby means of said switch.
 21. A vehicle in accordance with claim 1, saidvehicle further comprising: an information unit that informs said driverof the currently set target speed reduction rate.
 22. A vehicle inaccordance with claim 1, said vehicle further comprising: a failuredetection unit that detects a failure of said operation unit; and aninformation unit that informs said driver of detection of the failure.23. A vehicle in accordance with claim 1, wherein said operation unithas a mechanism that specifies the speed reduction rate by sliding alever along a slide groove formed in advance.
 24. A vehicle inaccordance with claim 23, wherein said operation unit has a mechanismthat continuously varies the setting of the speed reduction rateaccording to a sliding operation of said lever.
 25. A vehicle inaccordance with claim 23, wherein said operation unit is constructed toshare the structure with a mechanism for inputting a gearshift positionthat represents a selectable gear ratio range during a drive of saidvehicle.
 26. A vehicle in accordance with claim 25, wherein saidoperation unit comprises a first slide groove, along which said lever isslid during the drive of said vehicle, and a second slide groove, alongwhich said lever is slid to specify the speed reduction rate, the firstslide groove and the second slide groove being disposed in series.
 27. Avehicle in accordance with claim 26, wherein said operation unit has amechanism that increases the speed reduction rate with an increase indeviation from a movable range of said lever during the driver of saidvehicle.
 28. A vehicle in accordance with claim 25, wherein saidoperation unit comprises: a first slide groove, along which said leveris slid during the drive of said vehicle, and a second slide groove,along which said lever is slid to specify the speed reduction rate, thefirst slide groove and the second slide groove being disposed inparallel.
 29. A vehicle in accordance with claim 1, said vehicle furthercomprising: a gearshift position input unit that inputs a gearshiftposition, which represents a selectable gear ratio range during a driveof said vehicle; and a storage unit in which speed reduction rates ofsaid vehicle are stored in advance corresponding to gearshift positions,wherein said target speed reduction rate setting unit sets the targetspeed reduction rate in response to the operation of said operation unitand the input gearshift position by referring to said storage unit, andsaid selection unit selects the target gear ratio that attains thetarget speed reduction rate with preference to an energy recovery ratein the course of braking, irrespective of the gearshift position.
 30. Avehicle in accordance with claim 29, said vehicle further comprising: anaccumulator unit; and a detection unit that measures a remaining chargeof said accumulator unit, wherein said selection unit selects the targetgear ratio according to the observed remaining charge of saidaccumulator unit.
 31. A vehicle in accordance with claim 29, whereinsaid selection unit selects the target gear ratio in a specific rangethat prevents an extreme change of driving condition of a power sourceof said vehicle in a transient time from braking control to anotherdriving state of said vehicle.
 32. A vehicle in accordance with claim29, wherein said transmission attains a plurality of gear ratios setstepwise, and said selection unit selects the target gear ratio byallowing a deviation from the selectable gear ratio range correspondingto the input gearshift position by one step.
 33. A vehicle comprising amotor connected with a drive shaft and being braked by means of a torqueoutput from said motor, said vehicle comprising: an operation unit,through an operation of which a driver of said vehicle specifies a speedreduction rate in a process of braking with said motor; a target speedreduction rate setting unit that sets a target speed reduction rate inresponse to the operation of said operation unit; a motor driving statespecification unit that specifies a target driving state of said motor,in order to enable a braking force that attains the currently set targetspeed reduction rate to be applied to said drive shaft; a control unitthat drives said motor in the specified target driving state; and avariation unit that varies a possible range of setting of the targetspeed reduction rate according to a driving condition of said vehicle.34. A vehicle in accordance with claim 33, said vehicle furthercomprising: a transmission that enables selection of a plurality of gearratios in a process of power transmission; a selection unit that selectsa target gear ratio among a plurality of available gear ratios, thetarget gear ratio enabling the currently set target speed reduction rateto be attained by the torque of said motor; and a transmission controlunit that controls said transmission to attain the target gear ratio.35. A vehicle in accordance with claim 33, said vehicle furthercomprising an engine in a specific state of linkage that enables a powerto be output to said drive shaft, wherein said motor driving statespecification unit sets a target torque of said motor by taking intoaccount a braking torque applied by said engine.
 36. A vehicle inaccordance with claim 35, said vehicle further comprising: a connectionmechanism that connects and disconnects transmission of power from saidengine to said drive shaft.
 37. A vehicle in accordance with claim 36,said vehicle further comprising: a connection mechanism control unitthat controls said connection mechanism to disconnect the transmissionof power between said engine and said drive shaft in a process ofbraking with the torque of said motor.
 38. A vehicle in accordance withclaim 33, wherein said variation unit comprises: a decision unit thatdetermines whether or not a restriction condition to restrict the targetspeed reduction rate is fulfilled; and a restriction unit that actuallyrestricts the target speed reduction rate when the restriction conditionis fulfilled.
 39. A vehicle in accordance with claim 38, wherein saiddecision unit determines that the restriction condition is fulfilledwhen there is a slip occurring in driving wheels connected with saiddrive shaft.
 40. A vehicle in accordance with claim 38, wherein saiddecision unit carries out the determination, based on an operation of aswitch that gives an Instruction to restrict the possible range ofsetting of the target speed reduction rate.
 41. A vehicle in accordancewith claim 38, wherein said restriction unit restricts the target speedreduction rate to be not greater than a predetermined upper limit.
 42. Avehicle in accordance with claim 38, wherein said restriction unitcarries out feedback control to restrict the target speed reduction rateuntil the restriction condition becomes unfulfilled.
 43. A vehicle inaccordance with claim 33, said vehicle further comprising: aninformation unit that informs said driver of a variation in possiblerange of setting of the target speed reduction rate.
 44. A method ofcontrolling an operation of a vehicle, said vehicle comprising a motor,a transmission that enables selection of a plurality of gear ratios in aprocess of power transmission, and a drive shaft, which are connectedwith one another, said vehicle being driven and braked by means of atorque output from said motor, said method comprising the steps of: (a)detecting an operation of an operation unit by a driver of said vehicleto specify a speed reduction rate in a process of braking with saidmotor; (b) setting a target speed reduction rate in response to theoperation of said operation unit; (c) selecting a target gear ratioamong a plurality of available gear ratios, the target gear ratioenabling the currently set target speed reduction rate to be attained bythe torque of said motor; (d) setting a target torque of said motor toattain the currently set target speed reduction rate; and (e)controlling said transmission to attain the target gear ratio anddriving said motor with the target torque.
 45. A method in accordancewith claim 44, said method further comprising the steps of: (f)detecting a state of a switch that gives an instruction to executebraking with the specified speed reduction rate; and (g) allowing aseries of control operations by said steps (a) through (e) only in thecase where the braking execution instruction is given by means of saidswitch.
 46. A method in accordance with claim 44, wherein said step (b)comprises the steps of: (b1) determining whether the operation of saidoperation unit is valid or invalid; and (b2) prohibiting the setting ofthe target speed reduction rate from being changed when it is determinedthat the operation is invalid.
 47. A method in accordance with claim 44,wherein said step (b) comprises the steps of: (b1) determining whetheror not the target speed reduction rate is to be cancelled; and (b2)resetting the target speed reduction rate to a preset initial speedreduction rate when it is determined that the target speed reductionrate is to be cancelled.
 48. A method in accordance with claim 44,wherein said step (c) selects the target gear ratio with preference to apreset initial value.
 49. A method in accordance with claim 44, whereinsaid step (a) comprises the step of: (a1) inputting an instruction ofsaid driver regarding a selectable gear ratio range during a drive ofsaid vehicle, said step (b) sets the target speed reduction rate inresponse to the operation of said operation unit and the inputinstruction regarding the selectable gear ratio range, according to apredetermined relationship between the gear ratio and the speedreduction rate of said vehicle, and said step (c) selects the targetgear ratio that attains the target speed reduction rate with preferenceto energy recovery in the course of braking, irrespective of the inputinstruction.
 50. A method of controlling an operation of a vehicle, saidvehicle comprising a motor, a transmission that enables selection of aplurality of gear ratios in a process of power transmission, and a driveshaft, which are connected with one another, said vehicle being brakedby means of a torque output from said motor, said method comprising thesteps of: (a) varying a possible range of setting of a target speedreduction rate according t6 a driving condition of said vehicle; (b)setting the target speed reduction rate in response to an operation ofan operation unit by a driver of said vehicle to specify a speedreduction rate in a process of braking with said motor; (c) selecting atarget gear ratio among a plurality of available gear ratios, the targetgear ratio enabling the currently set target speed reduction rate to beattained by the torque of said motor; (d) setting a target torque ofsaid motor to attain the currently set target speed reduction rate; and(e) controlling said transmission to attain the target gear ratio anddriving said motor with the target torque.
 51. A method of controllingan operation of a vehicle, said vehicle comprising a motor linked with adrive shaft and an engine linked with said drive shaft via a connectionmechanism that connects and disconnects transmission of power to saiddrive shaft, said vehicle being braked by means of torques of said motorand said engine, said method comprising the steps of: (a) varying apossible range of setting of a target speed reduction rate according toa driving condition of said vehicle; (b) setting the target speedreduction rate in response to an operation of an operation unit by adriver of said vehicle to specify a speed reduction rate in a process ofbraking with the torques of said motor and said engine; (c) setting atarget torque of said motor to attain the currently set target speedreduction rate without the torque of said engine; (d) controlling saidconnection mechanism to disconnect the transmission of power from saidengine; and (e) driving said motor with the target torque.